The Ivorian endured an up and down debut season in London, leaving some supporters to question whether Arsenal overpaid on their club-record £72million signing.
But Lopez says the Gunners were lucky to get the winger for the price they did.
"Arsenal did one hell of a deal," Lopez told talkSPORT. "They got a player that other people wanted and they got a player who one club were offering more money for.
"It was Pepe's management team that asked us to go to Arsenal and so we accepted slightly less money than we would have got somewhere else.
"Some people know that, I know publicly some agents have said that but something that needs to go on record – we didn't sell him to the highest bidder."
And Lopez added that he is adamant the 25-year-old will improve next season.
"The second thing that is important is that talent is always there and you can't take it away from people,"
"He's a young player and a player that functions on people believing in him. Giving him opportunities but also responsibilities.
"I'm not going to question tactically how he was played for half a season. What I'm going to say is that, in his case, the best is yet to come.
"When he came to us, the six or seven first months were not even average. You could see glimpses of talent. He suddenly got into his stride in the second half of the season and he really came into it in the second season.
"I have no doubt that he can do the same thing. I watched him play in the cup game, for example. Yes his goal was not given but it was one of the top goals he can make.
"I watched him throughout the season, every time he gets the ball something happens. He's very tough to stop, especially when he's in the last 30 or 40 metres. You either have to foul him or he's going to make a pass or create a goal opportunity. That kind of talent is very rare. Players who on their own can dismantle or make something happen.
"I wasn't kidding when I said Arsenal got a good deal. Other people were willing to pay more and if he delivers, he can deliver, he can be a player who will be key to them finishing higher up the table."