Just dodge the Pink spear
This argument of dodge all of them is proof that you have no idea of what to problem is.
Can I dodge most of them? Yes but one of them given enough attempts will eventually hit. This ability is 25 / 30 / 35 / 40 / 45% (+ 8% per 100 AD) of your current health and/or likely 10 to 15 seconds of being at a disadvantage where you can't even back due to Tentacles spawning.
I would much rather see it changed to have a base damage on contact create the spirit for 3 seconds for Illaio and allies to attack with something like 15 to 25% + 5% for every 100 AD and it spawns one single Tentacle that tries to attack. That would make it over and done with instead of having to get creative with a extended curse. And it is the curse that is my biggest problem with this ability since it is kinda like a mord ult on a basic ability.