I feel this kind of runs along the same general line of argumentation as a great deal many threads that all start with "unpopular opinion" in the title: no, you're not the only one who hates laning against Illaoi, and in fact Illaoi is notorious for having a really frustrating laning phase to play against, particularly as a melee champion, with many threads on the Boards as proof.
I too personally agree with this, and I think the biggest problem with Illaoi in general is that her counterplay mostly boils down to her getting outranged. If her opponent can hurt her from a distance, there's not much she can do, but if they're close to her, she can walk all over them. Moreover, part of her strength comes from when her opponent stays around in the same place, since she gets to grow more tentacles. All of this obviously ends up not being all that healthy in top lane, where her opponent is typically a melee champion who's forced to stay in the same general area. It's also not that healthy for her, because after laning she generally feels useless unless the stars align and she manages to walk up to a team of players foolish enough to stay clumped together for some reason. Because of this, I feel she needs at least a few changes to be healthier to play against:
- Her tentacle damage should. Not. Stack. This I think is one of her biggest problems, because it causes her to destroy melee champions with her ult (who usually are at the center of all her tentacle slams), but otherwise means she's not that great when an enemy isn't getting slammed by multiple tentacles at a time, which is usually the case against ranged opponents. Removing the stacking component completely, instead of adding diminishing returns, would avoid her doubling down too hard on her punishment (more tentacles already means you have fewer safe areas to move to), and would thereby avoid situations where she explodes the top laner from outta nowhere.
- Her E target should be able to end the ability's effects by touching their own spirit. Not only would this allow her opponent to actually do something about getting caught, instead of just sucking up tons of damage for the next few seconds, it would directly mirror her Test of Spirit in the lore, in which people have to walk towards the spirit that was extracted from them and retrieve it. Moreover, this would allow melee opponents in particular to recover better, since they'd be closer to the spirit on extraction. Secondary changes I'd like to see to her E are:
- Remove the Vessel effect. It's not all that interesting or interactive, since even though it sounds cool on paper, it mostly just translates to "if you get this, you can't play the game for 12 seconds". It doesn't really give Illaoi more options, and only ends up frustrating her opponents more. It would also load her E less, since the damage transfer is already more than punishing enough as is.
- Allow the E projectile to pass through minions. This might sound counterproductive, since it would remove one remaining mode of self-protection melee champions have against her, but at the same time I feel this would affect ranged opponents more, as the latter are more able to hide behind the minion wave. Moreover, Illaoi typically uses her E on melee champions when they step out of their minions to last hit, so that situation would not be affected. Shifting the counterplay towards touching the spirit, rather than not getting hit, could end up making her feel more interactive overall, even if she could land more Es.
I think there's more to be said about Illaoi, and I do think the above changes could perhaps allow for buffs, as they'd mostly nerf her when she's not performing all that well right now, but the above I think could be a good start towards making Illaoi more fair to play against as a melee champion, which could then also help address her personal problems with how hard it is for her to deal with ranged opponents.