The FA paid a premium for a Champions League winner, a coach who had out-thought Pep Guardiola in a European final, precisely because Southgate's England kept arriving at the biggest moments and shrinking. The brief was never to reach a semi-final - England had proven they could do that with a cautious Englishman and a set-piece coach.
The brief was the last step, the game where a lead needs managing against elite opposition and the manager's decisions become the difference.
It's worth being honest about the road there, because it shapes the verdict. England's tournament was admirable without ever once being impressive. They won with 10 men at altitude in the cauldron of the Azteca, then ground past Norway in a quarter-final that needed extra time in the Miami heat and was unconvincing enough that Tuchel publicly criticised his own players afterwards.
Six weeks of resilience, problem-solving and clean-enough sheets - five wins and a draw in the six games before Atlanta - without a single performance that frightened anyone left in the draw. Which is fine, by the way, all while you're still progressing.
Nobody remembers how Argentina played in their 2022 group stage either. But it meant the semi-final was carrying the full weight of the Tuchel project: the moment the grinding was supposed to be converted into something Southgate never managed.
For an hour, it was working quite well. England's press was genuinely excellent - Anthony Gordon shut down Emi Martinez three times in the opening four minutes - and after a spiteful, foul-strewn first half in which neither side registered a shot of any kind for 30 minutes (the first time that has happened at a World Cup since at least 1966), England's control was quietly total.
John Stones and Marc Guehi completed all 63 of their first-half passes between them, and the half finished with expected goals of 0.05 to 0.02 in England's favour - a nil-nil in every sense, but one being played on England's terms. Then Morgan Rogers picked out Gordon at the back post on 55 minutes, and England led a World Cup semi-final with their first shot on target.
What followed was not a team being overwhelmed by a superior opponent but a team handing a technically superior opponent the keys and asking them to drive carefully.
Substitutes backfire
England managed just 17 per cent possession and nine touches in Argentina's half in the quarter of an hour after the goal, and Tuchel's response to that drift was to confirm it as policy: Gordon, the goalscorer and England's most persistent outlet, withdrawn for centre-back Ezri Konsa in the 72nd minute.
By then England had already been forced into 26 clearances since taking the lead, and Dan Burn and Nico O'Reilly followed on 82 minutes for Declan Rice and the injured Reece James - leaving seven of England's 10 outfield players defenders or defensive-minded, six of them centre-backs or full-backs by trade.
And the substitutes brought on to secure the game did nothing of the sort. The threat was real by then - Nico Gonzalez had forced Pickford's first serious save, and Alexis Mac Allister's header had cannoned back off the inside of the post - but Tuchel's answer to a mounting siege was more bodies and less ball, which is not how sieges tend to end, more how they are fed.
Konsa, introduced specifically to shore England up, failed to win possession back a single time while losing it five times, particularly when in threatening crossing positions. Burn's most notable contribution came after it was too late, redeployed as an auxiliary striker in the dying seconds of a game his arrival had helped concede.
These were not reinforcements steadying a wobbling ship; they were extra passengers on one already struggling offshore.
The numbers from that period read like a post-mortem. England completed just two passes between the 66th and 86th minutes - a one-two between Stones and Pickford in the 74th minute, which is less a passage of play than an SOS flare being fired.
Per Opta, England averaged 12 per cent possession between Gordon's opener and Lautaro Martinez's winner, while Argentina at one stage enjoyed 84 per cent of the ball, passing it around England's shape like training-ground mannequins.
England ended the night with 36 per cent possession to Argentina's 64 per cent and five shots to 15, and the xG tells the story of a game with two entirely different authors: from that cagey 0.05-0.02 first half, the second finished 1.57 to 0.47 in Argentina's favour - 0.52 to 1.59 across the match.
England did not lose a tight semi-final to fine margins; they surrendered one wholesale in the last 35 minutes, in a match that historically means an awful lot to both nations both on and off the pitch.
Gold for the GOAT
All that aside, the space England vacated went to the worst possible tenant. Lionel Messi completed nine dribbles and assisted two goals - the first player on record (since 1966) to do both in a single World Cup knockout game. England's entire team managed seven successful dribbles combined. Messi's seven touches in England's box matched every England player's touches in Argentina's box put together, as did his four chances created.
His two assists took him to 12 in World Cup matches, 10 of them in knockout rounds; no other player on record has more than eight in total. Records like that are not conjured against teams defending on the front foot. They are extracted from teams who have retreated so deep that the greatest player of all time is left to measure his crosses in peace, which is precisely how the 85th-minute corner routine found Enzo Fernandez for the equaliser, and how the stoppage-time delivery found Lautaro Martinez's head for the winner.
The most damning testimony came from the opposition, who described England's collapse not as something they engineered but something they were handed. Aston Villa keeper Emi Martinez, a man who has spent 16 years studying English football from the inside, explained exactly what Argentina sensed after Gordon's goal:
"We felt it. We felt them going backwards and backwards rather than going forward. Sometimes when you are winning, you have to go forward anyway. You can't change the game plan. I think they did it and they put extra defenders."
Lionel Scaloni went further still, saying England "doubted themselves" and that his side "smelt blood and went for it". When the beaten team's psychology is being dissected this fluently by the winners' keeper and manager within an hour of full-time, the tactical debate is essentially over.
Argentina didn't solve England. England dissolved, and Argentina, serial specialists in late escapes, did what world champions do to an open door.
'No regrets' for Tuchel
Tuchel's defence is that the match "changed completely" through no structural fault of his own, that England couldn't win or keep the ball and offensive substitutions wouldn't have helped.
As a description of the problem, it has some merit; Argentina's own changes, Nico Gonzalez chief among them, had shifted the game before he acted. As a description of the solution, it is self-incriminating. A coach who diagnoses that his team has stopped competing for possession and responds by removing his best presser and his best ball-winner has not treated the illness - he has signed the death certificate early.
The great in-game tactician, hired specifically for his in-game tactics, made the same read Southgate made against Croatia in 2018 and Italy in 2021 - the third time since 2018 England have led in a major semi-final or final and lost, and the only two instances this century of a team scoring first in a World Cup semi-final and failing to reach the final are both England.
Then came the line that will follow him to the Euros.
"At the moment, no regrets," Tuchel said in his post-match interview.
"The team gave everything, and we were very, very close. We deserved to be up 1-0. We played one of our better matches, maybe our best match in the circumstances."
No regrets about a semi-final in which his team completed two passes in 20 minutes?
No regrets about handing probably the greatest player ever the time and space to walk into the record books?
No regrets about withdrawing his goalscorer and most likely attacking outlet, still looking up for the fight, 1-0 up, and with a World Cup final 20 minutes away?
Tuchel simultaneously conceded England "got too passive" while insisting nothing structural changed. Nobody expects total self-flagellation 40 minutes after the whistle, but there is a canyon between protecting your players and declining to concede that hooking your goalscorer for a third centre-back, 1-0 up against the reigning champions, might at minimum merit a night's reflection.
Another missed opportunity
The bill for all this may take years to total. Harry Kane turns 33 this month; this was his fifth major tournament to end within sight of the summit, and by 2030 he will be 36 with a couple of dodgy ankles. Jude Bellingham and the generation behind him will have more tournaments, but they will not necessarily have this one again: a settled squad in decent form, a favourable route survived, and a final against a Spain side England would at least have arrived at with a puncher's chance.
Being 1-0 up against Argentina with 35 minutes to play may be as good as it gets for a while.
Tuchel was hired at considerable expense for one specific job, on the explicit understanding that semi-finals were the baseline he inherited rather than the ceiling he aspired to.
He matched the baseline, flinched at the summit, and proceeded to call it one of England's better matches.
The FA will keep him until the home Euros, and perhaps he will learn the lesson England's last manager never did. But on Wednesday's evidence, the revolution was merely a subtle rebrand. Sir Gareth at least had the decency to look haunted.