I also believe something is happening to write speeds when the SN850 runs on the X570 chipset lanes which does not happen to other GEN4 drives
But you haven't established that. You only tested the SN850, in two variants, 1TB and 2TB. If you'd tested other Gen4 drives on your system then we'd know this. But you haven't and so we don't.
I think the issue TheLostSwede has with you, and, frankly, I do too, is that you're making these massive conclusive jumps that are somewhat illogical. There's a hint of cognitive dissonance in your approach. What you do is telling us there's something wrong with the drive or the motherboard. Perhaps. You are however adamant that it can't possibly be user error. That you tried everything, absolutely everything and it can't possibly be you. Dealing with someone like this can be very frustrating.
You need to be more scientific in your approach. You are limited in what you can do, we all are, but you can be more thorough. Don't make a bunch of changes at a time. Be as granular as you can be.
Start FRESH, everything DEFAULT, NO overclocking of any kind. Whenever there's a binary setting that can have an effect on the performance of your SN850 drive, test with it in it's default state, then flip it, on or off, whatever that would be. Compare the results. Keep that setting flipped to the side that gave you the better results. Go to the next one. Non-binary settings require more time.
Take the time, do your research. Don't copy things other people did for their systems. Don't take everything at face value.
And don't get me wrong. It could turn out that you are right. You may well be right. The SN850 is a new product. Everything AMD does is and will forever be in a BETA state. But you didn't provide enough empirical evidence as to convince us to this end. Feeling it in one's bones isn't empirical evidence.