Vayne the problem must be solved

She got a nerf and still sitting on 52% win rate with a 19% playerbase. What I can't understend is: why her passive works during all kite process even when she isn't cheasing the enemy ? why her q can crit ? why varus has 54,7 ad al liv 1 without being an ipercarry, while vayne has 55.9 being a champ with a godlike lategame? why Tristana has this shi*t scale att. speed 0.656 (+ 0 – 25.5%) , while Vayne has this 0.658 (+ 0 – 68%)? why her stealth wasn't changed after the change to pink ward? why she can 3 shot people building ? why she has no real mana costs ( never see a vayne oom)? Why Lucian has 500 range being extremely mobile while Vayne has 550? why she plays different roles and she is the best in all of them? (tank shredder/ burst squishy/ self peel adc)