I honestly don't think "players will optimise the fun out of the game" is a good excuse to design the fun out of your own game first.

Players optimising the fun out of the game is their own choice and only affects their own experience. Designing jobs to chase the endless unattainable perfect balance affects everyone.

They should just design jobs to be fun and have their own originality and nuance while leaving whoever wants to optimise their fun out to do so.