I agree with your points,
Its the way rioto is trying to enforce diversity which bothers me. League unlike Dota2 cannot have champions that do more than one roles at any given time, for fear of said champion becoming broken and op in a role they were never meant to fill.
The best ROLE diversity we ever had was back in season 5 Around the MSI Patch, before the juggernaut rework. The following is an example:
Tanks (Malphite, Sion) = should be damage sponges and take a fair bit of time to kill, HOWEVER they SHOULD** NOT **BE DAMAGE DEALERS and should tickle, countered by sustained dps of marksmen and melee hyper carries.
Marksmen (Caitlyn, Vayne) = should be high damage dealers but incredibly squishy to kill by almost any class except tanks, and the only class that can siege turrets effectively lategame.
**Assassins **(Zed, Talon) = should be able to close distance and delete marksmen but be incredibly squishy themselves and be killed by anything other than marksmen
Mages (Malzahar, Syndra, Victor) = Jack of all trades class master of none, great for wave clear, team fights and pushing. Weakness late game.
**Bruisers **(Wukong, Riven, J4) = ad version of mages, Jack of all trades class master of none, great for wave clear, team fights and pushing. Weakness late game.
**Melee hyper carries **(Yi, Tryndamere) = Absolute highest damage in game, but susceptible to mage/tank/support Crowd Control.
Supports = Team dependent enchanter (buffs/debuffs), weakness relies on teams ability to perform and take objectives.