Firstly I don’t trust youtube videos. Secondly I have in the past installed MSFS to both PCIe3 NVme and PCIe4 Nvme both with and without Windows and can categorically say there was a significant difference in both loading times and performance. Ultimately I have reached the conclusion that both Windows and MSFS should be on your fastest drive along with your rolling* and manual caches while the package files should be on a separate, next fastest drive which can also double as a video cache.
Rolling* cache works wonderfully well on a ram drive and much better than none at all.