I'm just a player who mostly sticks to Manuel, but these are my thoughts as someone who doesn't really go out of the way not to go too far from your starting department clothing (usually only adding complementary items like a hardhat + highvis vest for CT for instance)
I feel like most people don't really stray too far from department clothing, if at all. I've noticed the more social jobs (usually service) or jobs like assistant are the jobs where people will go all out and won't even be recognizable at a glance as belonging to a certain department (which is fine IMO). Most other departments staff tend to just have complementary items, like scarves in medical, for instance. Perhaps this is some weird thing exclusive to Manuel, but I imagine it's the same on Terry and Sybil. Most customization I see is usually done with additional items such as hats and such, and only rarely do I see a department's starting jumpsuit get replaced with something else.
The nice thing is that people tend to stick to their department's color, outside of the rare scarf that's someone's favorite color instead of a department color. Not sure why this is, but if not for roleplay, then to at least not instantly get a toolbox to the head when walking into their department because their coworkers think that it's someone tiding into their department (trust me this exchange has happened a lot in my experience)
If the loadout PR thing that got greenlit were to ever go through, then I could get why the fat may need to be trimmed. On one hand you could probably stealth remove a bunch of the jumpsuits without people noticing. On the other hand, there isn't a particularly strong reason to do so other than the idea of having a lot of potential jumpsuits is seen as bad. As it currently stands I (in my uneducated opinion), I see it was a "yeah, it might be good to do that sometime in the unspecified future, but there's no big reason to do it." If there was ever some sort of massive change to the general art style that would require redoing EVERY SINGLE character jumpsuit sprite (or whatever the technical term is for how the clothes appear on a character's sprite as opposed to the item sprite), then yeah, sure, trim the fat.
"Spacemen playing dress up doesn't seem to fit the setting very much at all." kinda feels like the arguments that get put forward as to why you can't select what limb is the prosthetic one with the prosthetic limb quirk. I mean, yeah, it doesn't matter what limb the prosthetic one is, but it's a cool identifiable thing. Do you think TGstation would be as popular if everyone was forced into randomly generated characters every round? (this part went off topic, sorry)
TLDR I get the concern, but it seems unneeded IMO. It doesn't seem like there's a massive readability issue of not knowing if people are friendly or out of station hostiles at a quick glance, at least in my experience. Usually out of station threats are super recognizable. I don't think that should mean that the clothing roster can't be bloated, but it seems fine as is, at least in my opinion. Bloat is rarely good but trimming fat should have a solid justification. For instance, there shouldn't be 12+ types of functionally identical but visual distinct crowbars, but having some variations of crowbars is fine. Just like how jumpsuits are so insignificant that I don't really see an issue.