NT (which is what all versions of Windows is actually, just now at version 9) will use all the cores and HT cores to its advantage. How Magix effectively utilizes the resources is another thing. Vegas runs about 70+ threads, so its hard to believe that more thread handling would not be advantageous. If you are basing your opinion on CPU thread count solely on render speed, then that is not thinking big picture enough.
Rendering is a complex issue of system timing of decompressing frames, processing uncompressed data, then sending the results to the renderer. There are so many places where timing can get off and cause the system to wait on information from the upstream source. For example choosing a bad source codec to edit from. I think this why people complain about slow rendering. Most peoples systems are not optimized in terms of memory speeds, and other things, or they are attempting to use laptop hardware which is a joke generally.
The rule of thumb still applies if you go with 8 or 16 cores. 4-8GB of RAM for each core, that means 64-128GB of RAM for the 16 core ThreadRipper. With that much RAM and speed, you would want to be operating all SSD. M2 for boot and projects, or PCie SSD hard card. When you look into hard card pricing, that’s when most bow out and buy a cheapo SSD, then complain about not getting performance.