Its amusing reading some of the comments in the thread!
Ive a whole bunch of Canon
DSLRS, EF lenses and the EOS R with two lenses I own (RF 24-105mm f4L IS USM & RF 24-240mm f4-6.3). The RF 24-105mm f4L IS USM is better optically than its EF counter-part on the edges but not by much. The RF 24-240mm is what it is an average lens that needs in-camera or Lightroom / Camera Raw strong adjustments for vignetting and color fringing (chromatic aberrations). Its not a master class in lens design and one of their weakest lenses. The holy trinity we have in our rental fleet are all very good lenses that are marginally better that the EF lenses, the fast primes are good (RF 85mm f1.2L is much better). I can see no difference with EF lenses on the EOS R when using the adaptor both mechanically & optically apart from the spacing the adaptor produces.
As to Canon
teasing with the R5, working in the advertising & movie industry you have more impact if you "tease" close to the run-up to a product going on sale and make it available in good numbers the minute you do. If Canon
have any delays once they officially announce the price & on-sale date this will actually work against them not with early adopters but with impulse purchasers and could harm the adoption of the product. That coupled with a still limited range of native lenses in the RF mount (Rental like to have the f1.4 24, 35, 50, 85mm or at least these in a mix of 1.4 / 1.2) for a video centric mirrorless camera that the R5 is looking like it will be with 8K. Most stills lenses don't zoom well for video so primes are often preferred.