I seriously think we have to go by what we see on the screen. If dragon fire was meant to be as you imagine then it would have been visually portrayed but is wasn't. We've repeatedly seen death by fire and it's always horrific, whether it's Dany and her dragons, Stannis and Melisandre, or wild fire etc. In interviews GRRM describes the dragons as nuclear weapons and I believe Season 8 is going to fully look at the threat from Ice and Fire. Not just Ice vs. Fire.