With the recent change to Illaoi's E where she becomes "super oppressive" for a short time, It feels like that fantasy is being unfulfilled. The debuff is pretty short, unspammable and with the slow removed, everyone can just dodge your tentacles the same way they do on live, but with a lot more ease.
My change would be to keep it how it is, and to make the tentacles swing a bit faster near the vessel. Or, slowing the vessel ever so slightly whenever they're near a tentacle. Illaoi is slow as it is, and whilst she doesn't need anymore damage, ways to work around her E (now that everyone has figured out what it does) would be helpful. Mostly through the vessel part.
Another suggestion would be to reduce her E CD to where it could actually be a bit oppressive during her "vessel stage" or give her s slightly longer range, OR even giving her more recovery whenever she draws a vessel in as shes stunned for like .5 sec, then I think that would solve her current problem (which would be the "vessel" thing performing a bit less than what's reasonable and her E being a stun (don't know if thats intended) whenever she draws in a vessel. Makes 2v1's go horribly in your favor if you're unable to move.