Outside his ult, hasn't Maokai almost always been able to do that?
I don't want tanks more like amumu because we run into similar overlap. A lot of people wanted tanks to have unreliablilty in CC and damage like Sion, and that's effectively what we got in the update.
The overall heavier slows i see as an issue, as are displacements since they can't be reduced.
My problem with being like Amumu or current Malphite is that it doesn't feel like you do much after that ult, and sucks even more if your ult goes wrong because you don't have anything else. Beyond that, Amumu is poor without ally mages, and Malphite has to mostly W-auto and E. Last time I used Malphite, his attack speed slow felt like it didn't do much to the enemy adcs past laning phase, although that could be due to an abundance of burst.
I wouldn't mind less displacements for more meaninging debuffs overall..or pulling Cc from other classes so it's mainly tanks and supports that can have a lot, maybe mages with one. But right now, Mages have CC, Tanks have it, certain Juggs (but theirs is super limited, no complaints there), adcs have it, pretty much every class has some form of CC. Pull some of the CC from classes that don't need it (do Fizz, Talon, or Kha really need slows?) so a tank's CC doesn't feel overwhelming since they might be the only one on the enemy team with it, and also be willing to give tanks meaningful debuffs if extra CC doesn't quite fit.
And make tenacity feel worthwhile (even if Irelia's passive needs to change to allow that).