It's the opposite, your under powered until near 61. Once your 58 you can get two final skills which helps a lot. But good gear will become useless fast (even legends) within a few levels, so it gets really hard to maintain useful gear, but not impossible. Once your 61 though, you can get some good gear without worrying about it becoming under leveled.
It's just that enemies have 4x more health in UVHM, and they will always scale to your level, up to 2 higher. If you're level 61 for example, many bosses will be at 63.
In lower difficulties however, you can easily grind out a few levels until you're higher than the enemies in a certain area, because those enemies will always be locked to the level where you first entered that area until you defeat the last boss. Then, everything will scale to level 30 (Normal) and level 50 (TVHM).