I feel the real problem was the fusion of buffs toward tank items and nerfs toward that penetrate/shred/reduce, it made people "why am i building damage, these tanks are out trading me, they have more cc than me, I bring nothing by building full damage" however many people still enjoy a mobil play style so people went "you know what, screw damage, i'm just gonna build tanky"
TLDR
Tank items>Damage items
what I thinks needs to happen
Assasins needs to be made squisher, tank items needs to be nerfed so only tanks and bruisers will be building them, and damage items needs to be buffed.
This will be balanced because assasins will be easier to cc and burst down, they will be forced to build damage for tank items are no longer good on them, but with the buff toward damage items, they will now be able to compete against tanks and assassinate adcs. But at the same time assasin players will have to play smarter for they now know they can no longer hur dur press the R button and get kill. They have to now go "hey im squishy, I better play this smartly"
TLDR
what is wrong with this meta?
-Mid laners were incredibly nerfed, both mages and assassins.
-Ad carries one shot anyone who doesnt build armor
-Which leads assassins to build tank items
-Because Damage items suck, but armor/health items don't
-Which leads assassins to live off of good base stats to both kill and survive
Solution
-Nerf Tank items
-Do a massive buff to every tank towards their natural tank growth stats
-Do a massive nerf toward assassin base tank stats but compensate with a increase toward damage stats
-Buff damage items and ap items