Northern Ireland international Dallas was one of the key men in Bielsa's side as they won promotion to end Leeds' 16-year absence from the Premier League.
The 29-year-old has been converted by the Leeds boss from a winger into an attacking full-back.
"I just wish he had come here earlier than he did," said Dallas.
In an interview with BBC Radio 5 Live, he added: "That's no disrespect to the past managers because I have always loved working with whoever has been here, but in terms of my performances he has really improved me.
"I think I speak for 99% of the team when I say that."