It'd make for a pretty interesting situation where people could take it slow and steady or choose to challenge themselves by pulling more enemies than is recommended. Unfortunately the idea will be shot down by most people simply because they don't want dungeons to be anything other than a mindless experience with little to no challenge that can be completed as swiftly as possible.

It wouldn't be so bad if the content that requires more attention - such as Sophia EX - granted more tomes as a reward for completion over extremely easy 'Expert' dungeons.