Not at all. I'd give a lot to have that ability for my any of my fighters main weapons.
First, even at level 16-17, DC 15 will isn't "don't roll a one" for all enemies. There are still some enemies with will saves in the +9 to +12 range.
Second, if you're hitting four or five times a round, even at "don't roll a one" odds, that's still pretty good. The odds of an enemy not rolling a one in five consecutive d20 rolls is only 77.4%. If the enemy fails on a 2 as well, his odds of suriviving the round without picking up a curse are only 59%. If you get the weapon early enough that you face a foe with a mere +9 will save, that's a 42% chance of getting through the round uncursed on three hits (since you're getting it at lower level, I figure three hits is a good measure) and a 23.7% chance of remaining uncursed with five hits (for the lousy will save foe at high levels.
If you figure in a bit of finnagling to hit more foes--whirlwind attack or whirling blade in a large combat, you're almost certain to get at least one foe each round and likely to get several.
Individually, the hexblade's curse is a much more powerful ability because the DC is far higher. (I would expect a straight-class 20th level hexblade to have a DC of at least 30). However, since the cursespewing ability activates on every hit, it becomes tremendously powerful. (As will any effect that triggers a disabling condition on a hit--even if there is an easy save. Thundering is not broken because A. deafened is not really a disabling condition in terms of combat prowess and B. it only activates on critical hits which means that even in a best case scenario, you're talking one or two saves per round). If you want to depower it, I would suggest making it function on the first hit every round--possibly the first hit on any single opponent in any given round (which leaves more room for exploitiation with whirlwind attack, whirling blade, etc, but removes both tedious amounts of dice rolling for the DM and the "you're going to roll a 1 sometime this round" game which also gets old pretty quickly).
Crothian said:
The DC makes it okay in the low levels but a useless ability in the high levels.