My aiming really isn't great there though, and I lose lots of health cause of my not picking up shells before the fight. If you think this is near perfect you underestimate how well many players play quake (and those are the people targeted for Nightmare skill in Dwell).I think the degree to which it is a "puzzle segment" depends on your skill level, though, right? Your precision here is very high - I don't think you miss a shot at all, despite the rapidity of your aiming switching between targets whilst moving. So, sure, it's a puzzle segment (in terms of target priority)... if your execution is already near perfect. (If you think this is "sloppy", then...)
But anyways, Nightmare should require players to get things "near perfect" so that sounds about right, especially for this fight.
I think Markie did a good job balancing this fight for the different skill levels myself, been great watching people react to it so far.