I'd like an Illaoi nerf

No, not her unnecessary healing, nor her low cooldowns, or even her tentacle smackdown.

Her mana regen. She has "7.5 – 20.3" from 1-18. (Which in my humble opinion should be max "6-15.") Despite her meager mana pool of "300 – 980" she can spam almost non-stop for (and I counted) 23 seconds in a non-ending fight while still having over 30% of her mana pool remaining. This, coupled with even more healing from conqueror and Domination tree. (life steal and spell vamp) She loses all meaningful counterplay. She's tanky as, well, a juggernaut, with the capacity for 20-40% missing hp healing, coupled with 6-12% spell-vamp, and a never-ending mana supply. In general when up against a brawler/juggernaut with substantial damage and no built mana you just wait for them to tucker themselves out and then you fall on them. This simply doesn't happen with Illaoi, because her mana costs are substantially lower than her class competitors, and her mana regen is high enough to, for the most part, ignore the need to build any mana whatsoever.

Forcing her to diverge just slightly from a purely complimentary build if she wants overall sustain is hardly unfair, or even unreasonable. You can still build the same as you do now, but you'll have to be much more efficient or effective. Or you'll have to get some mana.