I know there are different level's of experience in the community. Veteran players have gameplay and build experience to make even the hardest difficulty a cake walk, while newcomers might struggle even on normal. For me, I've completed the game three times so far. During the last playthrough, the beginning and middle of the game was a lot easier than it used to be for sure. I guess I felt there was a difficulty spike near the end of the game a bit though. I guess I'll do another playthrough and mix up my build a bit and see how I feel afterwards. Thanks for chipping in everyone.
I don't think the disparity is difficulty related. I think it's related to what stage of the game you're in. In the early game, virtually nothing respawns, to the point where medsci1 basically stays empty forever, with the rare exception of 1 extra hybrid sometimes. Same with eng and hyrdo, which both spawn a little more but not much. Then there's that 1 spawner in command which is just ridiculous and pumps out spiders and rumblers constantly the moment you look away, but I think that was bugged.
I used to think the spawners were too low across the entire game, but I might have to revise that to say that they are probably too low up to recreation. After recreation they do get a bit more constant, and the enemies they spawn are much harder, so it evens out a little more. That said, outside of the ridiculous spawner in command1, it is probably still a tad low for my tastes, but I'm also a masochist when it comes to videogames.