You've just got to remember that guitars are made of wood and wood is not a consistent material. Fenders are also hand finished, so again not consistent.
There's not a whole heap of difference between MIM and MIA other than the hardware and how much time is spent finishing each bass.They use the same woods. That said, there are FSR (factory special runs) MIMs that may have had more attention paid to their build than US Standards.
MIJ is completely different kettle of fish. Different woods, different factories. Though their non-export models tend to be more like the FSRs in that they're made in shorter runs, better spec and build.
Squier again is completely different, with cheaper woods and hardware and different production techniques.
So... due to the inconsistencies present, even though these things are mass produced and that what's "better" or "worse" about each is entirely subjective, it's perfectly possible that a particular Squier guitar could be considered by the majority (if doing their best to be objective) to be "better" than a particular MIA. It's just that the odds are stacked against that being likely for each individual guitar.
I have an MIM, a MIJ and an MIA bass. They're all as good as each other in their different ways. Though my MIJ is a real beauty and my MIM is the best MIM I've come across.
So all depends what you think is value. And if you, for the sake of saving a few hundred quid (esp considering if you by 2nd hand, you're not actually losing "money") want to go though the likely process of buying a few MIMs in the hope of finding a really good one you like. Likewise, you might buy an MIA and find you don't... but in general, you're more likely to enjoy (if you prefer well built, finished and nice sounding basses) luck finding a good bass that's either MIA or MIJ. That, apart from their cost as new, is mostly why they hold their 2nd hand prices.
Like...
The Warmoth stuff is really good quality and consistent. The Mighty Mite stuff is good, and consistent, but not properly hand finished like Warmoth parts. They're not in the same league (or market) in that regard. All Parts I've not used, neither have I WD.