We aren't even in an assassin meta. We haven't had one since pre-Ekko release. Personally I'd love season 5, pre-sated or even the sated patches since both teams had it therefore it was "balanced" to a point. Darius, Skarner, and Garen busted? That's 3 bans not 11 needed.
Regardless, the game is still in a balance-able state. Giving most champions +2-4 armor and MR would fix many things, but other champions need more or changes to armor/mr-per-level too. Reducing lifesteal on Warlords and Bloodthirster to 17% (also lifesteal items costs and AD are reduced now), nerfing Lord Doms/Mortal Reminder, and removing and replacing critical strike chance would fix AD carries. Nerfing Morellonomicon and Void Staff while reducing costs of Luden's and Deathcap would fix many problems with mages. Reducing CDR on tank itemization would fix tanks. Making Sterak's Gage melee only fixes fighters because you can buff it, also make it stack with Maw again since ADCs can't have both. Assassins need champion fixes to fix the class. I'm not sure how to fix defensive supports. Though Malzahar's W change should be reverted so he doesn't work support.
TLDR:
Base resists up on everyone
down in lifesteal,
down in price by a chunk, 5 less AD.
nerfed. Preferably
is removed from the game due to being unhealthy.
Crit removed and replaced.
nerfed,
cost down.
less CDR itemization.
melee only, stack with
again.
need individual fixes.
revert the W change that made him support.