The problem is that you have a very powerful computer, but blender is not making use of it's resources.
Blender video editor is quite outdated and does not take advantage of the hardware. Limited multithreading and hardly any use of the GPUs capabilities. Blender is wonderful for 3D content creation, but the Video Editing side of the program is not robust at all, and has not grown to the meet the needs of today's users.
Try using a dedicated video editing app, like resolve free. With a setup like yours it should run smooth and problem free. No need to use proxies or transcoding.