Why is the best scaling champ in the game one of the safest

Nasus seriously needs nerfs, hes almost impossible to punish early when hes "weak" so 90% of games he just becomes a monster that shreds your entire team. Wither is honestly one of if not the most broken abilities in the game. It has like 4 seconds of downtime late game and is essentially the longest stun in the game. You literally have 1 movespeed and cant even aa him back bc for some reason it slows attack speed too. When a scaling champ with a weak early game is beating darius in a level 6 allin its a pretty good sign they aren't fucking weak early game.