Ahri is picked in over 1/5 games and has nearly a 54% win rate in Diamond
While also being picked in competitive play
http://www.leagueofgraphs.com/champions/stats/diamond/by-winrate
Darius was nerfed for less and he wasn't even being picked in 5s
Where are the nerfs
only gets hers if she lands one.
has less counterplay?
easily outsustains Darius and is a niche splitpush top.
amazing lategame scaling and can nullify darius' abilities thanks to his mobility and dodging
extremely hard kite potential and the ability to tank right through darius and avoid his heal factor.
Sure people consider those ranged champs toxic but there are plenty of melee champs that people consider toxic to play against as well e.g 
.