It might be because the aarch64 image was basically the same as the 32bit image just with a 64bit kernel added after. Which means xorg is more then likely still a 32bit package.
Both images was updated to the latest versions and the original Is was the latest from the raspi downloads page.
The 64bit kernel version uses the same amount of CPU usage as the 32bit version when dslstats is running and mine on both images hit 26% usage on Raspi 3B+. It also could be how XRDP was compiled as well to insure it works with Microsoft's RDP
Seeing the same behaviour on both the 32-bit and 64-bit Raspbian platforms is somewhat expected...what's
not expected -and in effect what I can't explain- is why the Xorg display manager consumes so much more cycles than the actual app...
Surely having DSLstats fetch data every 60'' or so "only" appears to push one core to at about 35-40% for a few seconds, however according to htop that's also accompanied by Xorg pushing another core to apprx. 65-80%, which surely doesn't appear normal at all (?)...In a DSLstats test installation I'm currently running on a new RPi4 for testing purposes over the course of the last 2 days I'm seeing 5h CPU time for DSLstats in htop and 11h for Xorg...(?)
I'd be inclined to install a 64-bit Ubuntu distro that came out recently for the Rapsi and testing it out if only I had the time to do so...