The second part of your post concerning "radioactive" and "poor" material is valid, afterall, this is actually a concern, but I wouldn't be too worried about that.
Do you think these factories just go seeking the cheapest 316L source from junk yards to make our watches? To produce watches and steel cases and parts on scale you would need a industrial supplier that are legitimate.
I think you overestimate how much money a factory can "save" by switching from legitimate 316L/904L steel suppliers in China. They're not scouring junkyards for the best deal on 316L scrap dealers to save like $15..... Additionally these kind of steel sources are horrible and you would be able to see material inconsistency, piss poor finishing and pitting on such type of steel....
I would be more worried about the cheap steel spoons and forks you have in your house that are from China.
There were rumors of some of these after market/off market tungsten cases having lead mixed into it which made it unsafe to wear but you don't have to worry about that if you're not wearing
Regarding "radioactive" matters I think you can safely eliminate this one. Of course you can always take a dosimeter to your watch if you want. I think a radioactive watch would already set off alarm bells through customs lol.
I recall seeing a material analysis of the steel used in Clean from a non TD and it was completely safe.