The "I know what I'm losing, I don't know what I gain, but it must be worth it" has the scent of fanboyism. At the very least, Canon's PR should have published what the gain is that they've compromised on no TC.
And the idea "the market leader dropped features from their new products for absolutely no reason" has a scent of cynicism. What's your point?
As I said, I won't pretend to understand enough about Optics to challenge Canon's claims. Canon has actually already published a number of marketing and white paper documents that touch on these subjects. From page 9 on the R system white paper, they highlight a big advantage of the new system:
"Large diameter rear lens elements that are much closer to the full frame image sensor —enhancing overall optical performance (in particular, tighter control over optical aberrations at image extremities)"
TThey go on to show how this is handled in the EF Mount and contrast it with RF on the subsequent pages, if you want to have a look. Here is the link if you haven't downloaded it yet:
The Product Showcases from Canon U.S.A., Inc. Explore the Canon products further and discover why these are worthy of your attention.
www.usa.canon.com