Maybe there is a slight overstating of the captaincy, but you could see the weight on his shoulders under Gerrard. I don't think Gerrard held McGinn back as an individual in the same way he didn't hold Ramsey back. He held the team back though, the sum of its parts.
McGinn hasn't just turned a corner since Unai arrived either, he's been dropped several times, had to get himself adjusted and regain form. Prior to that he was on most peoples lips as someone to replace. He's also playing predominantly the same position as under Gerrard, the difference though... he has a solid pairing behind him in Luiz and Kamara. The midfield is much better drilled and now easier to play well in if you do your own job.