Tries to roughly model a quick and dirty candle flame:
AgX Left, Filmic Right
Exposure 2.5
Exposure 0
Exposure -2.5
This is only very rough, using Blender’s internal Blackbody node for the color based on the temperatures in actual candle flames, but the intensities are most definitely wrong as I couldn’t quickly find data on that.
At least in terms of colors it should be roughly accurate though. (With the caveat that, from what I remember comparing RGB-based Blackbody output with spectral in the old spectral branch, the RGB colors aren’t that great)
At any rate, what you can clearly see here is, that at the very high end of exposure, the flame very very obviously does not match the surrounding cast color at all, whereas the AgX version manages this.
In the lower exposure settings, meanwhile, they are almost identical, but AgX already shifts a bit towards white, suggesting a brighter flame overall. It also does much better on the wick which transitions from red to orange smoothly rather than in a step.
Should also be noted, that these colors relate to skin tones too, so that’s rather important as well. Perhaps you are used to a (weird) yellow cast on flames, but that same situation on skin would be utterly unacceptable.