Obviously use whatever works for you, but note that the heavy processing does give benefit of storing only changed data in any given backup. It’s not by any means a file copy, so be careful what you compare with.
High CPU usage while backing up #2563 is an issue that just got more posts. One user went to restic to solve a CPU load issue (and I think its GUI is lacking, but that does do the upload-only-changed-data plan).
Big Comparison - Borg vs Restic vs Arq 5 vs Duplicacy vs Duplicati is one of several forum comparisons, and one where Duplicati seemed to be pretty fast. Yours is unusually slow, and the bottleneck is not clear.
Specifics are still vague, but if you have some other satisfactory solutions all set, there’s no need to push.