I hope the issue is completely overblown. I think the problem is the issue caught everyone by surprise, Canon is the company with a reputation for stability even at the cost of innovation and Sony caught a lot of bad press for their overheating issues, also I think the other issue is that thermal limits are far more unpredictable than time limits due to a variety of environmental factors. Last but not least, reports seem to indicate the limitations do not just affect 8K but also certain 4K modes as well.
I almost think if Canon had just set a hard 5min limit on 8K recordings and said that is that, then people would be more understanding. But when you really have no idea if you will get 20min or closer to 5min due to environmental conditions....that's where the problem lies, not to mention the long recovery times after entering this territory. As I have stated, I truly hope this is just a pre-production problem or that it will only happen in niche scenarios. In fact I still don't think we have any documented guidance from Canon at all in regards to overheating.
You say Canon is being up front about it, but I have yet to see any official documentation from Canon regarding the overheating issues. All we have is a leaked spreadsheet from a vendor that is still nowhere to be found on the Canon site. I have checked the official specs for the R5 and R6 as well as their sheets for what was improved over the EOS R - no mention of thermal limits anywhere in the marketing materials. So as of right now, if someone went to the site and ordered either of these cameras they would have no idea there is a thermal limit without first researching on other sites.
Nowhere in any of the links below was I able to find an official Canon statement regarding thermal issues (even in the fine print). So maybe it is just a pre-production issue, maybe Canon has not had time to develop an official message, or maybe even they don't know how bad it will be in real world use.
EOS R vs EOS R6 vs EOS R5 Comparison
EOS R5
High Image Quality featuring a New 45 Megapixel Full-frame CMOS Sensor. DIGIC X Image Processor with an ISO range of 100-51200; Expandable to 102400*1. High-Speed Continuous Shooting of up to 12 fps with Mechanical Shutter and up to 20 fps Electronic (Silent) Shutter. Dual Pixel CMOS AF II...
www.usa.canon.com
EOS R6
High Image Quality featuring a 20 Megapixel Full-frame CMOS Sensor.DIGIC X Image Processor with an ISO range of 100-102400; Expandable to 204800.High-Speed Continuous Shooting of up to 12 fps with Mechanical Shutter and up to 20 fpsElectronic (Silent) Shutter.Dual Pixel CMOS AF II covering...
www.usa.canon.com
I think the bigger issue is that no one knows how pervasive this problem will be until real world results come in and that Canon is known for reliability...even at the expense of innovation.