Its hard to say its the program if it isn't happening to everyone. But it honestly seems like they have done something that makes it run worse on higher spec machines. My terrible Lenova Thinkpad that is like 5 years old and shit tier specs runs it more or less fine. I have a few laggy screens and sometimes it will pass at the start of a draw. Very playable though. I would check your drivers, and probably just make a report to WotC for more information they can work with.
I'm on vacation (so you definitely don't see me posting) and I plan on digging into this more when I'm back, but I've been just playing as a customer and noticed something a little ironic. There is something to your theory that performance can degrade more on higher spec machines. We still have a number of per-frame memory allocations we are working on killing. So if you are running at a very high frame rate (I was around 250), you are allocating a lot more memory and, therefor, incurring a lot more garbage collections. Capping my FPS to 60 smoothed me out a lot. It's only one small piece of the puzzle, bit I though I'd mention it.