Tell me why Illaoi has more sustain than an assassin can inflict damage, without building tank or LS

[zombie-brand-facepalm]

She's a juggernaut. Assassins aren't supposed to be targeting her anyways. And learn to sidestep or buy Grievous.

Because she has no mobility no crowd control and can't really fight properly until she's spent time or her ultimate spawning tentacles, so her chasing and is really really bad if you move her away form her tentacles.

because you can dodge her sustain

and then she has none

She has zero mobility or CC outside of a small slow on E