That will most likely work.
That being said...we, as consumers, are very lucky. I remember not being able to film content because my ENG camera encountered too much humidity. I remember having to cover Blackmagic and RED cameras from direct sunlight to keep the sensors cool to minimize the chance of sensor noise. Apparently, A7s were known for overheating but I was lucky enough to not encounter that issue.
The projects I shoot for work and for fun allow me to let the camera rest in between takes. Having started out with a Canon XL2 and moving on to Sony ENGs, Cinema EOS, and ARRIs, it's generlly good practice to turn off the camera in between takes...at least to save battery power.
Every camera has it's quirks. Canon could have capped shooting options to 4K 30 fullframe but they decided to go ALL-OUT and let the thing over heat.
It's up to the consumers to take that risk and I'm one of them.
Now, if I have a paid project, I will have back up cameras and back up cameras for those camera and if the budget allows, I'll hire proper cameras.
If the R5 were a C-cam/crash cam, I'd pair it with the C500ii.
I digress but back to your comment, yes, at 4K 60p only, an external recorder may help reduce heat build up; the R5's card bay door even has heat warnings.
Signs are pointing to this being a sensor read issue, not a compression issue. It would help, but I wouldn't expect an Atmos to give you more than a few minutes of extra 4K-Fine