Some classes seem to reach a higher potential much faster than other classes. I do believe that depending on your class choices, this can have a major impact on the difficulty of main story boss fights and IMC has taken this in to account.
For example, I have a Level 32 Highlander that has killed up through Capria in 3-4 Cartar Stroke attacks. These boss fights are done in 40 seconds with no threat to myself. I have a Level 34 Krivis that has killed up through Capria and every boss is dead in 3-4 Zaibas, 1-2 Cure, 2 Heal. These bosses are dead in 75 seconds with minimal threat to myself, especially considering healing potential.
In contrast, I have a Level 20 Cryomancer that took 6 minutes to kill the boss in Mines 1F. The lightning totem takes a large number of hits to break, so none of the Wizard abilities help in breaking it faster. Overall damage is significantly lower with a higher cost in SP to use abilities that still don’t compare in damage output.
Now, I’ll agree that the difficulty of the bosses have not been high, but rather it was tedium as I had to slowly work down all those hitpoints, but supposing that the boss HP was reduced, it would have been dead in one Cartar Stroke. I believe that the bosses are tuned somewhat appropriately so that everyone doing the story should be able to clear the boss fights.