Veigo himself doesn't have to deal the killing blow to gain access to a opposing champions abilities and items?
MERELY a assist?
Oh yeah thats not broken at all.
Not to mention the reseting execute ult that you don't even have to actually kill with to reset it.
You actually can not set this champ behind in any meaningful way unless the ENTIRE team is behind.
It's Jinx/Kat takedown window (3s), not full assist.