Changes to onslaught...

I feel that for most players and reading forums its damn near impossible for them. So, I would say the life-steal debuff needs to go away, or lower cool downs on abilities and open all items up instead of the limited items. I tested 3 types of item sets and each one near the end was ridiculous. the Crit build jinx (no runans because that would be to easy....don't know why they didn't include runans with that many ads on screen) you can do alot of damage and kill things easily up until the 8th level however you then don't have enough hp to withstand 2 or more shots from vels. let alone getting 1 shotted by khazix constantly doing massive damage then stealthing. I tested a Tank version out and that gets you to about level 4 before you become a bullet sponge with zero damage almost so you are useless besides running around reviving teammates for them to insta die right after because they spawn with zero hp...and redemtion takes forever and a day to reset its cool down. The third one I tried was with lux. Built ardent censer and redemption, then ludens echo. I had zero damage to the boss and my shields didn't last more than 0.3 seconds before they were burst off my teammates.

TL;DR
Give us full Lifesteal buff without the negative 20%
or
Give us full item customization
or
Reduce ability cool downs a bit like automatic 40% that can increase to 60 if you buy the CD items.