illoai is ''fine''
i mean her main weakpoint imho is that she is teamcomp reliant. She eneds an extra initiator tank with lockdown and her team needs some extra cc aswell, and you are going to want some ap damage too.
The problem is when you realize that most of these cc heavy tanks are also played toplane. And they aren't doing so hot in the jungle because they get shit on by the likes of lee and nidalee
so that leaves support, and then you realize that out of the cc heavy tanky supps there is only a few with decent aoe lockdown
like you could pick nautilus and alistar for example becaus they can aoe cc, but in doing so they sacrifice peel ability for the ADcarry. So you need a self reliant ad carry.
Also since you want more then 1 guy to be able to enable her you are going to need either more cc/slows or other buffs and boosts
so you will want sivir or bleu ez
A mage with some aoe spammable shit which can apply rylais would be very usefull too.
And i think thats what makes her do shitty, she is very very strong except also very kitable/avoidable unless you have a teamcomp who can make up for the things she lacks
A sion would be very nice to have in that instance, but he has trouble competing with strong early game junglers when he is jungling and since you are taking illaoi toplane where would you put him?
Obvious answer is mid btw, sion mid with tp is really hard to deal with.
Tl;dr
Illaoi's biggest weakness is teamcomp reliance and the additional support she needs usually is played in the same lane she is.
And the big weakness really is the fact that she can only really be played toplane, because she needs the walls.
So how to make her work then?
Teamcomp:
I think illaoi can be strong with the right teamcomp as it is a nono to fight her head on.
so with a sivir adc for the utility and the fact sivir doesnt need a bodygaurd as much as other adc
A sion mid for the piles of cc he brings, he also brings waveclear and good initiation.
A jungle mage like malzahar or brand for example so your arent so ad heavy, and their aoe/dots can keep people from getting away once they get rylais
and for support a lulu is good because she has alot of cc and she can speed you up, or an alistar for good initiation and diving power or a nautilus the king of cc and he also has that neat point and click ult to start a fight.
Build:
but if your teamcomp isnt all you want then your build can make a difference too.
So since this
is allt he damage items you need, that leaves 4 other items to cover up some weakpoints
for example:
bring your own initiation
slow them down after you ult
lack initiation? make them come to you