Actually lock fear, DoTs, and life drain is terribly over-powered and there isn't much one can do against chain fear. Dispel (with cooldowns), but they just re-fear...
Rogues on the other hand. I had to go back and find quests I never went through with my hunter main, as even a year ago it was no big deal for me on a hunter to solo mobs that were 6-8 lvls higher then me. Bigger agro range? You bet.... But when one can get a sense of it, it's not that difficult to pull mobs far enough away to still be able to fight them in 1s or 2s. The only problem left is the pet would have trouble tanking a mob 8 lvls above it. But again being aware of agro, using means to drop it or increase pet agro, and using a threat meter can help.
On the rogue, fighting 2 levels above was much more the limit, and outside times where one could be funny like "along the watch towers", go up, sap the elite, mark tower, and re-stealth, fighting/killing nothing
But otherwise, I ended up having to find quests in zones I never messed with, because stuff like soloing Winterfall village at lvl 52 were out. Same with soloing "Dragonkin Menace" back when the dragonkin were still elites, at lvl 51.
I must say however, that at lvl 70, this situation does not continue. There are 69 elites that will kill the pet without healing. At this point mend pet is useless, and they will be a real mana drainer on any healing class. This is the point where I'm usually looking for a tank (or if I'm helping others on such an elite quest, insisting they get one in group). Besides, I'm at the point I can pull too much agro, too d*mned fast, without a proper tank and waiting for 3 sunders, etc, in such situations.
Mind though, while comparing hunters a year ago vs. now; pets were a lot more powerful then before they got normalized. Horde shamy used to hate my then un-nerfed broaken tooth in the lvl 40-49 BGs, especially when I would mana drain them on top of it