Yes it is so expensive.
compared to the 100-400 ii, 100mm more but increased to 7.1 instead of 5.6 for a much higher price .. i don't understand... that’s bad for use at dawn and dusk.
I'm trying to understand where the disconnect is coming from....
The EF100-400mm is f5.6 @ 400mm. If you add the 1.4TC it becomes 560mm @ f7.1. Reports have the RF100-500mm at f5.6 @400mm (depends if 1/3 stop or 1/2 stops are setup in camera) and 500mm @ f7.1 - so 60mm focal length different @ f7.1
"Bad' is basically a choice of ISO assuming constant shutter speed. Less light = higher ISO needed. R5/R6 have great high ISO performance so this is less of a concern. You could also say that the 500/4 is the only solution for your problem (EF400mm/2.8 + 1.4x TC) but that is at a big price differential again
From a price perspective, the EF100-400mm version 1 was USD1699 at release in 1994 and EF100-400mm ii @ USD2199 in 2014. The RF 100-500mm @ USD2699 so USD500 more after 6 years inflation and basically including a 1.4x TC (valued at USD500) in a package giving a 5x zoom. The EF100-400ii and EF1.4x TC are now cheaper than release price so the pricing seems to be more expensive but you would need to include the R mount adapter as well.
Digidirect in Australia have again got a 15% off sale including the RF100-500mm so equivalent to USD2294 to USD100 difference for a package lighter, smaller (with adapter), 5x zoom, sharper and faster to focus @ 500mm.
People seem to want a 200-600mm/5.6 but the Sony is f6.3 @ 600mm. The Nikon is maybe on their roadmap for next year but the aperture isn't known.