But yes, the science is fine if interpreted correctly. The correct phrasing would be exclude or not exclude a suspect. Or for your example, it could be consistent with someone having been in a vehicle. The problem is when the experts say they must have been in a vehicle, or especially a specific individual vehicle.
Second thing they teach in forensics is that unless I witness the actual event, it is really hard to tie it to a specific person. I can present dozens and dozens of circumstantial evidence which has sufficient weight for a reasonable person to make that inference, but I cannot attest to that.
But implying conclusions is exactly what both the defense and prosecutor are working at; they're constantly playing word games, and some judges would certainly be better than others at seeing through the B.S.
I'm not a forensic technician, but I've watched probably every episode of every true-crime forensic documentary TV show / YouTube channel / podcast / etc that exists; which probably has some weak but non-negligible correlation with having a gestalt impression of what people do and don't use forensic techniques for in practice. (At least in the "solved" cases, since the point of these shows is "how they solved it.")
In every use of "fiber analysis" I ever saw covered, where the "fiber analysis" was actually used to prove something, the thing they're always noticing is "trilobal fibers" — presumably because, at least for some period in recent history, those type of fibers only ever got used by specific manufacturers for specific use-cases (vehicle manufacturers, for car floor matting, IIRC); and weren't part of the composition of anything sold to individuals at retail (except, perhaps, replacement car floor mats.) So "trilobal fibers on the body" could be taken to imply "this person was at some point in a car footwell/trunk."
I don't ever recall any case that made a "fiber analysis" claim other than that particular one. (Maybe once someone claimed something about what proprietary dyes were used on the fibers via GCMS assay — but that's not really "fiber analysis" per se.)