Your initial post exactly corresponds to the thoughts I had when I decided, in conjunction with my recent change of camera, to give the RT internal browser and rating system a chance (instead of using a lame DIY system of manually created best/ directories, sometimes containing another best/ directory and so on 
).
Now I extract the embedded JPGs and look at those via a basic image viewer on one screen, while having RT on another screen to apply my ratings and to trash what deserves to be trashed.
Stupid Bash script leveraging exiftool to get the JPGs from CR3s:
Code – Expand to reveal
# For logs and to stop if something goes wrong.
set -ex
exiftool -b -JpgFromRaw -w '.jpg' ./*.CR3
exiftool -tagsfromfile %d%f.CR3 -orientation ./*.jpg
mkdir -pv jpg/
mv -ut jpg/ ./*.jpg
# Get rid of backup files that pop up at some point.
rm ./*original*
Of course it’s more a workaround than a real solution… My main complaints is that it doesn’t show clipped highlights, and that the resulting JPGs don’t seem to contain the values for aperture, speed, ISO and focal length, which I have to seek in RT directly (that latter point may be fixable with extra exiftool commands, though, but I haven’t bothered to try yet).
It seems there are lots of topics about this “culling” process and how painful it can be (regardless of the derawtizer involved, it seems):
Initial culling of raw images, Culling photos fast, etc.