Why the fuck is Vayne a champion?

True damage, tank shredder, insane mobility, a stealth, a knockback/stun, increased movement speed towards enemy champions, and busted lifesteal. Sure, this seems healthy. But Riot doesn't want to lose the autistic players Vayne mains because they get sweet sweet dollar bills from all of the skin purchases. This is coming from a mastery 5 Vayne with more than 50k mastery points BTW, so don't say I've never played the champion.