There is a ton of examination on the R5 going on around the web, and your information would be the first example of a new problem, and the reception to it would be much different here.
Without any sort of evidence, your experience runs completely against everything that is available out there (and there is a lot out there), so I can't imagine why you'd be surprised at it being received with a whole lot of doubt.
His report is not the first example of a new problem, but rather another example of a known problem. And his experience is in line with what's available out there. Stills shooting can drive HQ video record times to zero in 80-90F weather. It would be foolish to assume that stills alone could never drive the chipset to thermal shutdown, especially in hotter weather.