You have to be a really dedicated rep watch nut to spot the difference between 904 and 316 steel (and there's always arguments over whether it is even possible). As to the threads stripping - I have no idea where that notion came from, I've never seen anyone complaining that their crown threads stripped because their watch wasn't made with (Chinese) 904 steel... The reps TDs are selling have very good quality stainless steel cases and parts, no matter which version steel your rep is made from. I have ARF and Noob Daytonas, and I fall into the "can't tell - don't care" category when it comes to the component steel.
I'm not sure SOLEX has made things much clearer for you, so I will also add:
1) I don't think the Noob 4130 movement quality is necessarily inferior to the 7750, but the 4130 is more likely to fail - because it's a fully working chrono movement, and it is also newer to the market. Servicing the 4130 is also expensive, should you wish/need to have it done. It cost me £160 to have mine serviced, and it can cost more, depending which watchsmith you go to. But you're not "on your own" if it goes wrong - because it's a clone of the gen 4130, a good number of watchsmiths here on RWI and the other rep forums can/will work on them.
2) The chrono partly works on the ARF - the big seconds hand goes round when you use the chrono.