Can't say respawns ever annoyed me. "right behind your back"? Literally, I've never seen that in dozens of replays. If you mean something coming down a hallway you've come from, sure. But never in a situation where I would go in a room, walk out, then immediately go in again and find an enemy the second time. Whenever it happened, the enemy always came from some well-traveled corridor that it could plausibly have come from if the ship was really crawling with them. Overall I thought the spawning was actually pretty weak up until the Rickenbacker. If you are being surprised I think you are being too fast rushing around, not listening and/or peaking around corners.
Yes, guns are basically unusable at the beginning due to lower ammo efficiency (damage per bullet) and low ammo availability/lack of repair. This is obviously intentional, most of the Hybrids are specifically made to be dispatchable with melee while the robots are designed to be what you need to save your ammo for. Wrench hit detection is perfectly fine, stop being shit. I can clean out the med deck with a wrench and have a 50/50 shot of taking no damage, there's no excuse if you can't comprehend simple timing to move forward while your hit connects.
You talk about finding enough tools eventually, you DO know that you can buy maintenance tools from the beginning of the game, right? Hack the very first replicator in the game, it costs like 90 nanites. And that's on impossible difficulty, on normal I believe they cost half that (45). You should have several hundred nanites available by the time you finish the med level. Pistol can fire IIRC 10 shots for each level of durability. Yes it's still silly that they break, but if you have anything over 1 maintenance you have no excuse for running out of tools. And anyone using tools at 1 maintenance should probably just go ahead and kill themselves.
Repair skill is indeed shit though, you should basically never take it because simply maintaining guns before they reach 1 durability ensures they never break. The few broken things you want to repair can be repaired by the automatic units.
Vote OP for faggot of the year.
About the weapon degradation in SS2... yes, it's broken. There is no arguing around it. When sci-fi weapons work less reliably than 17th century muskets, something is horribly wrong. I wonder how that bs passed QA. It constantly rips you out of immersion, because it is just so utterly unrealistic.
I think the problem is more that (AFAIK) absolutely no weapons in the game come fully repaired, and the vast majority of them come with 1 or 2 durability. A fully-functional pistol will fire about 100 shots before breaking. It's still unrealistically low, but 100 shots is a god damned lot in gameplay terms. It would be interesting to think how perceptions would change if most guns started off with 9 or 10 durability but finding repair tools was much harder. But even still, if you exercise an ounce of thought weapon maintenance should never be a problem.
IIRC there was a planned audio log that would have explained that The Many had created some kind of biological containment on the ship that caused machinery to break down, but it never got put in.