I leveled most of my jobs together with my partner - one of us would pick a dps, the other a tank or healer (after each set done, we'd switch). So even if one of us disliked the particular job they were leveling, we were still doing it together with daily leveling roulettes, which made it barable.
For our most hated jobs - monk for me, dragoon for my partner - we just went for the slow pixie-grind on the side.

We also didnt rush it, which probably prevented the burn out - knowing that we had 2 years before the next expansion (and the next level increase) made it easy to take it slowly, but steadly. We're both done for a couple of weeks now.

So... not doing it alone and only in small doses (one leveling roulette per day, beast tribes and hunts) did the trick for me.