[qbrass]

Without taking gender into account, the word relentlessness sounds more like a negative trait than a positive one. They're someone who's unwilling to deviate from their plan of action, because their plan is to just head straight for the goal.

I'd go with dauntlessness, someone who's dauntless won't let an obstacle stop them, but will go around it instead of through it.

[SudoNhim]

That's dodging the issue though... the issue was that relentless is apparently masculine. What if they say the same thing about dauntless?

I don't think relentless has to be as mindless as you say. Someone who gets in the zone and attacks a hard problem 20 different ways until they solve it is relentless in my books.