I agree, illaoi`s kit requires her to either
A: have teammates that cc/distract/peel for her to get her combo off...which is unlikely given that she is filling the top lane slot most of the time.
Or
B: One or more players on the enemy team needs to be ignorant and not used to fighting her.
If either of these scenarios are satisfied she becomes extremely powerful either by nuking group fights with her damage while the enemy team is amumu stunned or just her simply being too fed where a single stray tentacle could chunk you.
As illaoi, if you are fed to the point where your damage is obscene, there are scenarios where you could ULT when you see someone running away after you land an E on them and nuke them since any tentacles that appear around them when they become a vessel will also slam faster and be almost unavoidable for immobile champs.
And there is the other issue, if she gets ahead she poops anyone who doesn't have an escape...
Riot should work on giving her more interaction with playing the actual champion and have the player target areas where they want each tentacle to slam one at a time (basically treat her tentacles as actual skillshots that originate from them)
Then nerf her damage a bit so players don't get deleted and instead see their healthbar get chunked a bit more steadily. (while taking into account that illaoi has more control over her kit now)
This would increase the skill cap on illaoi by a massive amount while giving the player more interaction than W auto W auto W auto, it would no longer be an easy game of just dodging her tentacles and removes the extreme worst / best case scenarios for her when the enemy is ignorant / knows exactly how to avoid them.