i've been thinking, would a thief and maid of light be in more or less of an eternal stalemate? since the thief could forever steal the maid's luck... but the maid would keep regenerating it since they're Made of it

But see, the trick is that.

LUCK DO3SN’T 4CTU4LLY M4TT3R. >:]

Even with all the luck, Vriska and Terezi’s confrontation came down to whether Terezi would Act or not, not how much luck Vriska had. Likewise, their abilities may imply a stalemate, but it would come down to whichever of the two is more powerful, their actions, their motives, and what they focus on regarding Light- Fortune, Light itself, Information…