How important is here to really burn it? Is ISO VM booting regarded as a reliable test or not? (Note: We don't burn classic Fedora images when testing either.)
I would want to, yes. I do burn classic images when testing; the tests https://fedoraproject.org/wiki/QA:Testcase_Boot_Methods_Dvd and https://fedoraproject.org/wiki/QA:Testcase_Live_Image_Boot specifically require writing the images to media.
Oops, and I was doing it wrong all the time.