(skeptical)

Fire is a fluid simulation and this has been in consumer tools like houdini for a long time now. Even in avatar from 14 years ago there were plenty of CG explosions that people didn't think about.

The moment you comp it in to a live plate our uncanny valley spidey senses kick in

I haven't seen this be the case if the scale is right and the resolution is good. After that it is a matter of compositing. There is actually a decent amount of cg fire out there now. I found this after 10 seconds of searching on youtube:

https://www.youtube.com/watch?v=1Ec3hrkwh8Q

Doing live action integration is tough in general, but fire is additive and that helps quite a bit. LEDs that can be add lighting to the photography helps too.