You know, from the cheapest of cheap pickups, to the most expensive of expensive (around $300)...over 45 years of guitar playing, swapping etc, I have never had a pickup crap out on me because of the materials, or construction or anything.
As for US vs Asian magnets, I would venture that an A5 magnet is an A5 magnet, wherever you get it. Might be some variation in size, shape, strength, etc. It is not unusual for some products to be tolerance sorted or binned, however.
Take pots. Typical 500k pot might be +/- 50k. But you can order 'binned' that are 500k +/- 10k or whatever.
Still, except in exceptional cases I'd guess a charged A5 bar is a charged A5 bar regardless of country of origin, unless you really paid more for a specific charge - however they measure that.
All American-Made is usually just a marketing deal to get you to pay more
A5 from Asia = 12 cents in bulk.
A5 from US = 14 cents in bulk, but you get charged an extra 5 dollars because of that.
Suddenly you are paying an extra $250 for a $50 pickup that cost an extra 42 cents to produce.