well the high scalings are not a problem, that said its not that high scaling very often and they have to go melee
and building full ap means they are no longer a tank so thats kind of healthy as opposed to full tank fizz who still murders everyone
Anyway i agree with you
Tanks aren't defined
In my opinion we need more diverse tank roles/niches
In order to do that a set of subclasses would be nice, and some reworks to make certain champions fit these subclasses, they would have to fit there thematically
One such a subclass im thinking of would be the behemoth, a tank equivalent of the juggernaut sort of
Now this would be the strenghts
It would have high base damage and strong scalings,
Hybrid damage to make itemixzation against it a bit more difficult.
Very potent CC
A strong scaling lategame, gets very tanky
Early game, level 1-5, bully potential but not that strong in allins at this point. A possibility to start rolling early on if not dealth with.
And possible other strenghts would vary between champions to fit their niche
And this would be its primary weakness.
Highly unreliable, but each and everyone of them should have at least 1 reliable thing they can do, whether its being extremely tanky or a reliable engage tool or some other for of utility.
Like 90% of their kit would be very unreliable and therefore this means they have a high risk vs a high reward
Another weakness would be lack of mobility outside of an engage tool.
Other weaknesses would vary between champions.
So who would fit this description currently?
He has the potential to unload a ton of damage for a tank and has piles of cc he can also get very tanky but literally everything in his kit is highly unreliable, which is one of the reasons he isnt picked much, currently he lacks a bit of reward or reliability i have my own idea's how to fix this but lets not get into that now
Other possible champions who would could be reworked into this category in my opinion.

Well thats just one subclass of tanks that could exist
And there would need to be vangaurds, primary engage champions with tools to start fights
Wardens who would focus more on protecting or buffing their team
The support tank lack of damage made up with reliability in utility
I think in generall all tanks would need high base health and good base resistances and base sustain with itemization available to counter the various damage threaths or provide some team utility through aura's
Itemizition that would synergize with their high health and resistances and therefore be less likely to be abused by champions who lack this base health and resistances