Sinque, I see what you're trying to do here, but it seems like a rehash of The Community Improves Heroes or Controversial Heroes, only for a narrow (and difficult to decide what to put inside of it due to subjectivity) category. Really, it's not that tanks are a bad class in KR, for, classes don't even exist in the game. It just so happens that tank heroes tend to be poor in combat compared to other (that is, the heroes that we generally consider tanks).
Of things not yet mentioned here, the first and biggest problem that I see with allowing all tanks to block 3 enemies is that Ironhide has no way to satisfying us with tha definition. This thread is small as of my post and it already has arguments for what heroes to classify as tanks and which ones not to. I could say that Kutsao belongs on your list of UP tank heroes, but I'd feel hypoctrical since I don't want to count Durax or Lynn as a tank, based on my own personal interpratiom of what tanks should be classified as in KR. No matter what heroes have changes made, there will always be disputes over which ones to take that power away from and which ones to give it to.
Second, rebalancing heroes in order to have this capability may as well just be reworking the heroes like in the TCIH thread. I'd find it a lot cooler if instead of Grawl getting even more HP and being allowed to block 3 enemies, he just had his Hard Rock skill replaced with a skill that allowed players to use him in a unique way that would result in multiple enemies being blocked.
Admittedly, you could say that all that's required for Catha to block enemies is to just move her into a group of enemies, let her summon her pixies, and then fly away, but it at least has some more finesse to it, and she doesn't take quadruple damage from doing so. I do agree that the tank heroes should be fixed, and I'm open to the discussion delving more into tanks in general and what to do in the future (like what the one paragraph about KR4 was about) instead of debating the details of what heroes count as tanks.
For that line of discussion, I'm fine with my idea of using skills to implement more effective ways of blocking enemies, since, it
would make it easier to create more interesting heroes with lots of new, unique abilities.