Normally I'd say 'they're not actually starfleet' but...
WTF.... I just... Don't understand.
Actually, I don't think that SB-80 personnel is incapable or untrained (otherwise the station wouldn't have survived as long as it has)... they appeared to have lacked the means to do the necessary work for the most part.
If you take away an engineer's tools, do you think they'd be able to fix issues?
I doubt that.
The personnel on SB-80 is likely in a pinch where they make due with outdated equipment.
Even if they had 23rd century era style technology, its likely possible those tools broke down and needed to be replaced - after all, tools do end up broken or worn out from use.
Plus, think about it for a second... these people were trained in the mid/late 24th century to work with MODERN technology (mostly), and then they find themselves working on tech that's over 100 year old. Sure, they'd probably be able to do the work in the most basic sense, but without the proper tools or even modern diagnostic equipment, it will be difficult to do so.
Also, its a freaking embarrassment for SF to have anything that's over 100 years old. Sure, an exterior shell is one thing, but the insides? Come on. The station should have likely underwent upgrades around 2360-ies.
You wouldn't expect of modern engineers to work on outdated systems and hw unless they were specifically trained in historical preservation etc... and while I have no doubt that SF Academy covers historical knowledge (it does), as I said, its likely that without modern tools they would barely be able to keep the station running.
Tricorders are usually needed to diagnose problems on a deeper level than what your eyes alone can tell you.
I suspect Gene Jakobowski and other engineers were capable, but simply lacked the tools to carry out the needed work - so when the Cerritos crew came onboard looking for a nav processor, he made use of them - since SB-80 has a bad rep, no ships seemingly want to stick around long enough to lend a hand or the needed resources (which is really bad when you think about it).
Its also possible that some of the people volunteered to go to SB-80 (like the El-Aurian commander) while others were transferred because they couldn't make it work on their usual postings - that or, they were directly shipped to SB-80 because the station technically 'needs' engineers to keep it running - but again, SF has just dropped the ball on it heavily because they sent 0 resources so they can actually do the work - its sort of like a bad catch 22 situation (at least in regards to SB-80).