I should probably clarify my remarks about f/11. I wouldn't for a moment suggest that f/11 should not be used for bird photography, which is clearly silly. And clearly Canon could be expected to endow an f/11 prime lens with very good optical quality. But this is not the same thing as it being an ideal lens for birds, or beginners.
My point is more that a lens with a maximum aperture of f/11 is going to mean significant compromises, particularly if the light is anything other than bright. Either you need to slow the shutter down (and risk motion blur) or increase the ISO to very high levels. To some people, these compromises are going to be acceptable, to others not so much. I expect that Arbitrage is very experienced in managing these things, and seems to be able to do fine bird in flight photography at relatively slow shutter speeds.
I note that many of Arbritrage's images are all taken at ISO3200 or higher. I am not sure how well Canon's R series work at high ISOs, but it seems to me that if you are constantly having to working ISO6400 and above to get a sharp image there must be some impact on image quality. I am using APSC so its completely different, but with Canon's most up to date sensor I find that ISO3200 is really pushing it, and I am also finding that even f/5.6 is a bit slow/dim for photography in many situations if I want to use shutter speeds of say 1/800 s and ISOs below about ISO2000. Unless I am reading it incorrectly, Arbitrage is using a top range Sony camera, which will likely perform differently from a Canon in any case.
Beyond that, I'm not really sure what his images tell us. He is using a top range G spec zoom lens with an extender, which really won't tell us anything about the performance of a newly designed budget prime. His images don't really tell me more than (a) you can take good pictures at f/11, which is not in question, and (b) he seems to be a pretty good photographer, so he could probably take good images with just about any system. Unless I missed it in my quick scan, he doesn't say anything about use of tripod etc.
Whether the compromises involved with an f/11 lens make it a good choice for birds, or a good choice for beginners, well, the jury is out for me. My initial reaction is that it would lack the necessary versatility. But all power to Canon's arm - I presume they have done their research. But I did smile at this quote from Canon's website about the EOS-R system: "The EOS R system is born from Canon's pursuit to create faster, sharper lenses for unrivaled image quality. Taking advantage of mirrorless design and new RF lens mount allows flexibility to engineer lenses that were previously not possible." Hmmm
Regards
Simon