I see a lot of confusion so let met precise something.

Difficulty is not time-consuming. Time and difficulty are 2 separate and different things.
Most of the time, something time-consuming is not difficult : when you bash mobs for example. You simply do the same thing over and over and over again.

A way of defining difficulty would be the planning it requires before you do/fight something. Another would be the amount of errors you can make before wipe, or more precisely the amount of damage you take when you make mistakes.

Anyway the 2 concepts have to be separated.