To folks who feel the video time (thermal) limitations of R5/R6 are a deal killer, I feel your pain. I’d have felt the same way to learn, for example, that 12fps shooting was limited to 25 shots without AF. But rather than rail against the Canon beast, I’d simply look elsewhere. Or wait for what I need to justify spending $4,000.
I think, and just my 2 cents here, that Canon clearly prioritized the R5 and R6 as stills cameras. The many stills shooters who worried the R5/R6 would sacrifice their needs for amazing video specs were wrong. Now, the video-centric crowd can see that, in fact, it was the exotic video specs that were compromised (time-limited) by Canon's engineering commitment to a small, powerful, weather-sealed stills-first body.
I don’t consider time limits on video shooting to be defects. They are simply engineered limitations that may or may not work for some. The same applies to still specs. These decisions were all tossed around in Canon development meetings, you can be sure.
I'd also suggest that most of the nearly-unbelievable pre-intro hype for these new cameras did NOT appear to come from Canon, but from social media and rumors, and perhaps, insider leaks. Canon did tout the full-frame 8k capability to a convention of broadcasters a few months back, but I never read it was without limitations. In fact, there was much speculation on this site about probable 8k limitations and for most people it was generally expected In some form.
In hindsight, Canon PR/marketing could have done a better job of pro-actively dealing with the video overheating limitations during the official launch activities. For example, proudly claiming the advancements but acknowledging limitations that, by design constraints, would not be acceptable in certain applications. Better to crap a little on your own parade rather than be covered by a giant dump from the interweb “Influencers.”
I think these will be superb cameras for many shooters (As will competitor's products). As always, our mileage will vary. I'm happy we have so many great choices for our various needs.