At any point have you checked Logs in the app menu or using journalctl?
I agree with you. Given your specs and hardware, you should be enjoying smooth sailing.
I do not think that Gnome or Wayland are the cause. But what I think is that Gnome-Shell has some corruption in its install that is not enough to be critical, but is enough to cause a memory leak that is causing you CPU spikes and constant headaches.
Something small... A misconfigured file or value... And sussing out what it is and where it is is no small task.
If this was me; I would save myself that kind of nightmare.
I would back up all personal data and do a full reinstall of Zorin OS 17.3
(Actually, I would install Zorin OS Lite 17.3...)
I know that seems daunting; but to resolve and issue, get a fresh clean start - it seems a good idea, to me.