They have slightly worse stats than arial warriors (who fall into the similar dex-build category) but they have their own advantages over arials.
1) Can use gear. Arials are limited to a few not-very-good pieces of arial-only gear. And drow/elf only eq is advantage, not disadvantage.
2) Sneak. Which is great. I repeat. Sneak is great. Sneak is great.
3) faerie fire or quick strike(?) in general are more useful than arials inherits.

Arials can fly, but some cabal powers of potions may help elf/drow warriors in this respect.

Speaking of stsf. I will repeat myself, it can't be balanced in its current shape.
It's like liches, they are OP, all you can do is not to give them to skilled players to maintain balance.

In most of fights stsf warrior has time to charge it. Especially in raid situations.
If it will be possible to charge stsf, people will do it and become overpowered.
If it will be nearly impossible to charge stsf then the legacy will be useless. Like Mercy of Typhoon.

And noflee part of stsf should really go away, it's overpowered. Charged stsf provides you with something like dance+ward legacies, maybe something else and makes those standalone legacies almost obsolete for elf/drow warriors.