The first character I played, I kind of meandered through skill trees randomly and found myself getting slaughtered around level 15 or so.

My second character I focused on two-handed, incidentally leveling light armor, and he did pretty well (even managed to kill that frost troll on High Hrothgar).

My current character I'm trying my 3/2/1 strategy, with one skill (one-handed) kept highest, two secondary skills (conjuration and alteration) kept at 2/3 the value of blade, and three skills (Restoration, Destruction, Block) kept at 1/3 the value of blade. He's really not all that tough.

A good fourty hours into the game, minimum (didn't actually check my stats), I still haven't wrapped my head around how to level characters properly (as in, in a fashion that does not result in enemies at higher levels being far more powerful than me). Or is that even the issue?

Also, I read at UESP that once you've entered a dungeon, the enemies are locked into the level they were when you first arrived for the rest of the game. Is this true? If true, does it hold for all enemies? Because I remember trying to "level past" Vokun, who was absolutely tearing me apart at lower levels. It didn't seem to work; ten levels later, he was still owning me (until I figured out that the trick is not to face him directly, but rather simply to snipe him from behind the columns to draw his fire and let Anska do the real work). But shouldn't I, at some point, have attained the ability to absorb the damage he was dealing better and dish out enough that I could actually go toe to toe with him?

Dragon priest are one of the few enemies who have a set lvl which is 50, so go lvl up some more before face him and try to focus on lvl up a few skill say 1 weapon, 1 armor so you don't get underpowered later on you can get over to a second weapon skill.

Ah, so THAT was my problem with that first character. Dragon priests were killing me dead everywhere I went, and I thought I was running into that "improper Oblivion leveling" type problem.

So what's the deal with Anska? Why is she so powerful?

I often find that things get significantly more challenging around level 15 or 20. What I do when that happens is to reassess and upgrade my gear through smithing and enchanting. Also that's around the time I feel the need to toughen up magic resistance or elemental resistance. I will move off guardian stone and take up lord stone for extra protection for a while. 25% magic resistance is like increasing your armor 200 points against magic users.

Anska i don't really know she is not set lvl she does get stronger depending on your lvl but i guess she might have something like oblivion guards that she's always + 10 lvls or something that's my guess anyway.