Maybe I´m missing something significant here, but Hummels playes the exact same role as he did since the season 2011/2012. He is our primary build up player, vital for the team in that regard. He is now simply in a proper form which can be seen the most in his passing game, which is back to its usual level.
Thomas Tuchel is an amazing coach, who certainly deserves a lot of credit of setting up this team. However, IMO the most important reason why Thomas Tuchel is the ideal successor of Jürgen Klopp is that he openly honors the foundation which the latter has built for Borussia Dortmund. This can be seen by looking at the squad, which did not underwent the massive overhaul which many predicted. It is still a quality squad, which normally belongs in the CL and the top group of the league.
Furthermore, Tuchel did not temper too much with the teams DNA. Today the team showed supreme pressing, a lot of hard work in terms of movement and quick transitions. The last two goals used to be trademark goals of the era Klopp. Rather than radically changing the tactical set up, Tuchel builts on said foundation, fleshes it out and makes it more flexible. He identified the weaknesses of the team (passing accuracy, composure in ball possession, width) and worked on that while keeping the old strengths intact.
In the end he manages to do what most supporter hoped when he was appointed: creating the right impulses for a struggling team to bring them back to their best. Klopp could not do that anymore after seven years, which is no shame given that such long tenures have become extremely rare in modern club football. This does not make Tuchel the way superior coach or some kind of messiah, though, although the media likes to paint it that way with the neverending comparisions. It makes him the more suitable coach for the club right now.