Well, Zac was really one of the worse champs back then and he is still now, going from a small pool of champ to be viable to all the 120 champ pool to be viable is a bit of an unrealistic goal to meet, his pick or Ashe jungle pick not being common is not just something that can be pointed out as Riot's fault
And, if you see, half of those troll picks champs aren't anymore considered troll picks anymore: Fizz is considered one of the most powerful champs and we even saw Ad Fizz recently played by UoL (!!!) - In that game in the video he was builded AP - , Rammus, Maplh are not troll picks anymore, Jarvan is right now one of the most OP and banned champs around, so what si lacking, imho, is not the variety from season to season, but the variety in the meta of a specific season (which is also players fault, though, there are a lot of off-meta picks that counter meta picks which are rarely used by both pro and common players)