Illaoi is too strong a support
Illaoi is an extremely oppressive support. She can easily have both the enemy bot laners as empty vessels. Additionally, since the cooldown of the spell is shorter than the minimum time it takes to remove the debuff from killing tentacle spawns, she can instantly re-vessel someone when they get back to lane. An empty vessel is all but guaranteed because her adc can sit back and burn down the spirit safely while Illaoi either runs away to avoid damage or assists with crazy AOE + healing.
Something needs to be done about how overbearing E is in a duo lane. I recommend ramping the contribution from teammates: 0/25/50/75/100% so that Illaoi can't invest in damage as much if she wants her adc to assist in taking down spirits. Basically, spirits would get damage reduction when hit by other players until max rank.
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. Also as an ADC you have a huge range advantage on your side, effectively making her tentacles free gold for you. Sorry, but I just don't see how Illaoi support is more oppressive than any other support. She's got 0 CC and 0 peel for her carry and she is completely immobile and easy to peel. All you need to do is play smart and it's so easy to make her useless.