Designing classes so they can clear content as quickly as possible seems like a bad idea to me.

Personally, I don't care nearly as much about how long a dungeon takes as I do about how long it feels like the dungeon takes. I'd much rather spend half an hour playing a job I found interesting, than fifteen minutes spamming the same spell.

So if we make "fastest clears possible" our design goal...that sounds to me like an admission that the game is never going to be fun, and that the best we can hope for is to get our tomestones and get out. In which case, why even play?