Looking at ranged rogue vs. Warlock. I'm assuming the rogue always has a sneak attack target (which isn't going to be true) while I vary if the warlock has hex up. The numbers in () are the damage if the blast only can add once.
Code:
[B]
Level Rogue Warlock Warlock
no hex hex[/B]
1 10 5.5 9
3 13.5 8.5 12
5 18 19 (15) 26 (21)
9 26 21 (16) 28 (23)
11 29.5 32.5 (22.5) 43 (33)
17 40 42 (27) 56 (41)
I think it's fair to say that the rogue will have a sneak attack more often than the warlock will have hex up. Given the initial damage relationship, I'd say that the intent was that warlock with hex would track rogue. At level 5 even with the more limited rule of once-per-blast the warlock is ahead of the rogue (+3). It's +8 with RAW. But level 5 is a really nice one for the warlock. Level 9 is a bit more fair. And there it is something closer to a tie. At level 17 things are very much weighted in the warlock's favor. At a point when the warlock has a significant number of non-at-will options. (Lots of quite powerful spells)
Basic theme: it all depends on which you think has the stronger package of other options. I'd claim it's something of a tie for a while, but nothing compares to casting higher-level spells (though if doing that, the warlock is unlikely to have hex up that much). I'd say both work, but RAW is probably a bit on the high side.
Suggested rule: The stat damage should be nerfed to apply only on a per-target basis. If you shoot 4 rays at one person, they get the bonus only once. If you shoot at 4 different targets, you get bonus to each. I think it's a good compromise.