I seem to recall a storyline in the comics a few years back about the Rebel Alliance commandeering a Star Destroyer but it ultimately not serving them much good since the Rebels couldn't spare anywhere near enough personnel to operate the thing properly. Which I imagine is a similar situation here, the New Republic only intends to operate a military a mere fraction the size of the Imperial military, and as such won't have enough personnel to properly staff even one Star Destroyer.
Well also keep in mind here that the rebellion absolutely would (and probably did) use captured Destroyers if given the opportunity. It's a rebellion after all, and they can't exactly be picky about where they get their hardware, especially not when it of that magnitude. It's quite a bit different once they've won and trying to set themselves up as a legitimate government.
But yes, there is a certain impracticality with trying to adapt an ISD for peacetime use. Aside from breaking the last hold-out warlords, I can't see the NR having much of a need for orbital bombardment, or the need to launch massive mechanised ground assaults.
It seems to have been quietly revised out in later editions, but the initial version of the Cross-Sections books implied that the first Imperial (or, at the time, Imperator) Star Destroyers were already in service before the Clone Wars ended. That's still possible in the canon, I know some novels had them showing up practically immediately after the Empire was founded, but I was always struck by the image of a classic Star Destroyer in Republic colors. If that had been the case, it'd be an even harder sell that the New Republic using them would've been a legitimate change, as opposed to just showing that "SD" stands for "same shit, different day."
I think the earliest we've seen the ISDs is in Fallen Order which is about 5 years after the Clone Wars. Though even that appearance is a little dubious given they seemed to just borrow the BF2 asset from DICE, which is based on the eight footer from 'Empire', not the original three footer in 'A New Hope' as it probably should have been.
Speaking of ships, I noticed some new markings on the X-Wings. I'm pretty sure all the ones we've seen in "Mandalorian" have had the same Red Squadron insignia from the OT. It's not a big variation, I think it was just a different color stripe, but it's something.
I was hoping that we'd start seeing a wider variety, maybe using the designs from "Squadrons."
Yeah, I noticed the T-65s in the prison transport's hangar had a blue stripe along the fuselage that wrapped under and around the belly, just behind the torpedo tubes, as well as a semi-large NR gold starbird seal a little further back on the flanks, between the cockpit & engine intakes.
Given that the A-Wings in that hangar similarly have blue markings and a seal on the tailfin, and that the Lothal E-Wings shared the same markings, plus of course the blue flightsuits and uniforms worn by both these soldiers and the police on Corellia (which may or may not actually be CorSec), it's a fair bet that this is simply the standard livery of NR security/judicial forces (likely evoking the Republic Senate Guard of old.) Indeed I'm pretty sure Kaz's NR marking in 'Resistance' were basically the same.
By contrast, while it's tough to make out what their markings were, the X-Wings flying CAP for Home One didn't seem to have those blue security markings at all. The ones on the hangar at least seemed to have green markings; no nose stripe just the belly wrap-around. So there could be a distinction between security forces and the actual military.
Which incidentally would make the Rangers under the military, since what we've seen of them seems to be split between different red & green marking schemes.
The difference would be if they suddenly made Return of the Jedi a prequel to the previous movies. Yes, the saga is "out of order", but only to a point.
People naturally assume that, since Ahsoka appeared in previous shows, that naturally her own show would occur after those appearances.
If they were to mess with that, it would seriously (and needlessly) confuse everyone for arguably no reason.
It's not as confusing as you're making it out to be, especially since you don't have to have seen one show to understand what's going on in the other. Worse case, there's some dovetail exposition down the line that places when this is happening relative to Mando, but it probably won't even be necessary.