You write very authoritatively (and literally boldly) for not actually being very correct. This isn't meant for reheating cooled coffee. It's meant for maintaining temperature. Yes, technically it is actively adding heat into the system, but it's at such a slow/gentle rate that it does not noticeably diminish the flavor. It is nothing like a burner plate on a cheap coffee machine, or the microwave. James Hoffman has an interesting and informative
video on this subject, if you don't believe me.
I'm about as big a coffee snob as they come, and I daily drive an ember mug. I can say for a fact it does not wreck the flavor. In fact, because it keeps the temp in just the right range, it actually enhances the overall flavor profile over my drinking duration (usually around 15-20 minutes).