When Illaoi gets released

Ummm... no. she is not op.

The tentacles have 800 attack range, and lanes on rift are 1000 units wide at their thinnest points (the corners of the map in top and botlane are much larger). They cannot attack quickly. Tentacles are capable of swinging once every 10 seconds against spirits and vessels, but otherwise do nothing until Illaoi hits a unit with her W. If you are a vessel, the tentacles will spawn wherever you go, yes, but their attacks are incredibly easy to dodge and they die in two hits. Illaoi has no true damage in her kit, and the rest of that sentence doesn't make any sense. As a support, Illaoi is trash. Ranged champs negate her passive if they have enough brain cells to right click. She has low utility, and saying that she can "ONE SHOT THEM" with her soul stealing is bullshit. Even at max rank, it only carries over 45% of the damage dealt to the spirit, and they will only die to tentacle spawn if they are either not paying attention or they don't know what Illaoi does.

Her level 1 damage is not that high. Her passive is meaningless because she doesn't have her W yet, and her Q at level 1 deals a whopping 10+120% AD.

As for there being "literally no way to counter her", here are some ways to counter her. Kite her. Kill tentacles. Dodge the fucking skillshots. Run out of range of the spirit ASAP. The Vessel mark is worth avoiding the damage, since you can clear it by simply killing 3 tentacles. Ignite her. Don't let her build up tentacles. Don't fight in her tentacles. Bait the ult. Camp her (seriously. She has no defensive mobility, and no readily available CC. She can't escape without flash, and if behind, she provides next to nothing due to her lack of utility) Get armor. CC her. Stand behind a tank so she can't E you. Play a ranged toplaner, since you will negate her passive. Keep teamfights on the move. She is reliant on staying near her tentacles, so taking the fight away from those devastates her.