To me, KAY-O looks fucking strong for the following reasons. Congizant I may have missed something. Let me know your opinions on why you think he'll be broken or not good. I state my case below.
His flash is the most versatile in the game
doesn't need a wall like breach
doesn't need to bounce like yoru
doesn't need to be guided and can be destroyed like skye
doesn't require close proximity to corners like phoenix
doesn't have a range limit and can be destroyed like reyna
This flashbang will be the only TRUE popflash in the game that is literally unavoidable if people learn lineups, like in CS
His nade is a more viable molly than any molly in the game as you will do higher damage per tick even though ticks are slower. Most mollies you can get out of and take like 5-10 damage, won't be the case here. Also more effective for zoning cause it lasts longer than raze nade
His knife literally gives info on HOW MANY you suppressed and WHO you suppressed as well. Jett in a one and done angle? Knife goes by, she can't dash out or use smokes. Imagine KJ on ascent B with that alley molly setup. "KJ suppressed rush in", kj cant stop the push. Can also be used JUST for info
His ult disables all abilities, gives him reyna/brim combat stim and allows him to be revived when down. When he's down he's got 850 hp so impossible to kill his downed body fast. Literally use him like a phoenix to get into site without the ability to get flashed while doing it, and you don't have to hold his body like phoenix.
Literally everything he has except for the knife and the emp part of his ult is a similar or better equivalent of existing util
EDIT: Edited to say he's got 850 HP when downed.