Drow are not "low level" monsters. They are "high level" monsters that should strike fear into the hearts of adventurers of any level..
I would totally ignore the CR 1/4 "soldier guys" [I guess?]. Your "basic/low level drow shmo" should be the CR 5 guys.
But it's so much more fun to kill PCs on a budget of 1000 XP. The mooks are almost as good as the elites if you use them right, and a whole lot cheaper.
Among other flaws in the official system, players advance in level more quickly when they have equivalently hard combats against fewer foes as opposed to more foes.