I think it'd be more effective to bring back Naoto Ohshima, because the core problem the team has seems to be figuring out just what the hell Sonic is and why people liked the games in the first place, just from a presentation level. That's honestly the main issue the series is facing -- figuring out how to present itself. Yuji Naka would be a great benefit though, because he has a mind for physics in programming, and I could see that aptitude being good for leading a team of programmers on a Sonic game. If I'm being honest, I think the unsung hero of the original Sonic Team was Hirokazu Yasuhara, the director and lead game designer for the Genesis games. I love Sonic CD, but his absence was sorely missed on that game and it shows in comments on its level design to this day.
The point I'm really trying to get around to is that Sonic Team found an incredible balance of talents and visions that came together to form a cohesive, brilliant unit. The current situation is a mess. I have a tendency to blame Takashi Iizuka because I think he has a lot of bad ideas, but the problem is much more complicated than that because game design is far more complicated today than it was when Sonic Team was formed. So in terms of fixing the gameplay... I'm not sure, but the gameplay really isn't all that bad. The issue is with presentation and direction.
Get everyone together and have them watch the Sonic OVA, go back to the roots and reacquaint yourself with the environmental story-telling of the Ohshima-centric Sonic CD and the original Sonic 1 level order (the settings originally went from least to most industrially developed but was changed around because Labyrinth was a bad second Zone), get input from Hirokazu Yasuhara and Mark Cerny, and COMMIT to going back to the roots and move forward organically from there. The "new" Sonic has been a failed experiment. And that's fine -- it happens in a creative field, and it even made a couple of good games, but the half-measure of reminding us that there was a version of Sonic that wasn't over-complicated, was visually unforgettable, had universally liked character design, had meaningfully implemented gameplay hooks, has not aged, and can still be relevant... and then presenting it as a gimmick side-product is missing the point by a mile.
Go back and commit to that Sonic. That's not a gimmick. That's your product, that's your legacy, that's what you need to live up to.