Champion who's gimmick is that he gets insane buffs from his ultimate but you lose control of him

Dumb idea, basically i thought of a champion concept that involved having a q, w, and e that all have high cooldowns but with really strong effects and the character would play like a tank. But his ultimate would make it so he gains 90% cooldown reduction, some tenacity and damage etc. but the catch is that You lose control of what he does while the ult is taking place and it lasts for something like let's say 5 seconds. I sort of thought the idea of getting really overpowered buffs from something would balance itself out if the player had to trust the ai, most likely the ai wouldn't even target low health champions, just whatever is closest. But again, he's now spamming spells that normally have 20 second cooldowns every second as well as having some cc reduction. what are all your thoughts on all of this? and how could i refine this concept into a champion?