Not sure I follow you.
You want affordable 600+mm lenses but don't like the current small/light/affordable/sharpish RF600/800mm primes.
Assuming that the RF100-400 will not be a "L" lens then it will be cheap and cheerful
The price for the RF100-500mm will drop. I got mine on a 15% off sale. Still expensive but getting closer to a current EF100-400Lii + 1.4 TC + R mount adapter. It is amazing for a 5x zoom.
It seems that you want cheap, fast, long focal length and I can't see that happening anytime soon. Don't forget that you can adapt all the EF lenses from Canon, Sigma and Tamron etc.
What i want is something middle range. Like Sony or Nikons upcoming 200-600. High quality, weather sealed lenses but still on the affordable side and not super dark like the Canon cheap primes.