I play a Mercenary Bounty Hunter and I completely disagree with this issue with bolster. Even with 50s on my team, I am often easily beaten by a brunch of lvl 20s (I'm almost lvl 40 ATM). On the flip side, I have had no problem killing level 50s at any level. Just learn your class, use interrupts, stuns, knock backs. Keep on the move, run behind people etc. Lvl 10 to 16 is usually the hardest, as you don't have a lot of this CC, but once you get it, ere really is no problem.