I would say that Torment's combat really isn't that hard. I found Dragon Age: Origins incredibly hard at times, just on Normal, but I never had any problem with Torment. Spells like Cloudkill - or the Abyssal Pipes that you can use to cast it - make the latter stages of the game a lot easier. Not to mention that fact that aside from thugs randomly attacking you, you barely
have to fight anyone at all. I agree that it takes a lot of DEX to get any armour class bonus, but I just found TNO gets hit almost constantly with low DEX and that his regen was never quick enough to keep him alive, only to heal him between battles, until you get CON really high at the end of the game. I know not everyone will, but if you play with the Tweak Pack, one of the recommended tweaks is to always get the max possible HP at level up (so that's 10 for TNO, regardless of class it seems) and so the HP bonus from CON loses its edge.
As another tip, you actually get bonus permanent stat boosts when you reach 7th and 12th levels with a class. You only get the bonus once - so reaching level 7 with a fighter means you won't get a permanent stat boost when you get to 7 with the other two classes. Also, say you take the level 7 bonus with the thief, but then reach level 12 first with a fighter, you won't get the level 12 bonus. You need to have already got the level 7 bonus in a class to get the level 12 one.
Fighter: 7th + 1 STR, able to have 4 proficiency in a weapon. 12th + 1 STR, + 1 CON, + 3 HP, able to have 5 proficiency.
Mage: 7th + 1 INT. 12th+ 2 INT, + 1 WIS, + 5 Lore.
Thief: 7th + 1 DEX. 12th + 2 DEX, + 1 Luck.
There are also quite a lot of other ways to get permanent stat boosts, outside of simply levelling up. I'd post the list here but it arguably contains spoilers (characters and locations, mainly). You can find it in
this FAQ by searching for
Mortuary, Starting Level. Also, in the same FAQ, you can search for
CRTNGN to see a description of the various stats and the kind of uses they have.