It seems like with Illaoi's E it should be easier to fight her 1v1 in lane.
Given that 2 of the 3 outcomes of test of spirit are becoming a vessel (soul killed or you run away, with soul fading being the third), and that it doesn't have a prohibitively high cost like a blitzgrab, it feels like fighting her if she hits you should be a little easier.
Right now it feels like only the tankiest of champs like Malph can fight her at all and post 6 getting E'd just like, auto means you lose a big chunk of your health, eat the slow, and have to deal with vessel or die if you try to fight.
Feels like pre6 Illaoi should at least need her minion wave to ensure a favorable trade.