Loctite, as a company, wouldn't make that claim if they couldn't support it. They'd get sued like crazy every time there was a failure. From an engineering standpoint I would bet the published capabilities are well under what that material is actually capable of doing, just for legal reasons.
As for what feels loose, that's completely subjective isn't it? No one has said to use loctite no matter what, the hub has to be measured so it can be determined if the Loctite 660 is a viable repair. It may not be in this particular case, but that doesn't mean it's not a useful product or that other people may not be able to use it successfully.
You think the "interference fit" doesn't cause some wear to the hub when you replace the races? What about the studs? The forces they apply to the hub will eventually wear those holes. Certainly removing and replacing studs is something you can only do some many times before you need oversized studs to achieve the proper fit.
My point is that while serviceable, the hubs do have a lifespan even when everything is done properly. And all it takes is one race to get a little crooked when it's being installed to cause tolerance issues later. If everything is done perfectly you can replace a whole lot of races before the hub will fall out of tolerance, but not everything is always done perfectly. And over 50+ years, **** happens.
