I'm playing a level 33 assassin on Expert.
My skills are dual-wield, archery and sneak (as main skills) supplemented with restoration, light armor. That's about it.
You should be able to go through a perk tree as you play without it breaking the game 1/3rd of the way through.
With a dual-wield of 70, archery at 68 and sneak at 73 and with significant perks in each tree - I almost never, ever die. I don't use enchanting (I'm using a 20 shock bow I found at like level 10 or so), I don't use alchemy, I don't use smithing on my swords or my armor.
I have an Assassin-type character as well, who plays pretty much like this except I allow smithing. Unless I massively screw up he's effectively immortal, and I don't even have the best gear yet. Dragons are about the only challenge, since they're a bit harder to sneak up on, but with a bit more practice I'll be able to gank them too. My Mystic Archer is even worse; she's level 66 and has end-game uber-gear, and can one-shot almost anything in the game from long range.
In neither case did I do anything contrary to their RP or play style, yet in both cases I have a character that can trivialize almost any encounter. The only reason I haven't increased the difficulty is that I play Dead-is-Dead; at higher difficulties the chance of being one-shot out of the blue increases dramatically, and I don't have the option to reload if something out of my control gets me killed.
Part of me wants to see this fixed, but I don't really expect it to be; fortunately, the characters make up for it by providing really good RPs, so I actually come out ahead in the exchange.