Not sure why Larian opted for 18m for everything.
It's simpler that way, obviously.
On topic: why so much STR? Just for jump distance? Considering that Thief is the biggest bonus action spender out there, I don't see much benefit in this. At first glance, without actually trying, I would prefer WIS for Perception / Insight, if nothing else...
But yeah, interesting. Drow are natural assassins, but in 3.5 this was countered by photophobia and +2 level adjustment. Here, they just come out as OP as they could possibly be.