DH is 1 of the hardest classes to level, if you start from nothing. There will be a point where you feel really weak, then you unlock some hatred management skills and get a lot easier. And at end game, you will feel really strong.
So, once you hit that point, don't get discouraged, just lower the difficulty and keep going
As for your time, just enjoy the trip and the story, as you will probably never return to story mode.