The feature works the same on iPhone. Looking through my duplicates just now, the detected duplicates that had a dozen or so photos to merge, are either high speed sports photography bursts or astrophotography—the rest were just mostly two photo duplicates. I suspect the threshold for determining a the photo as duplicate is too high for successive* photos to be considered such, as with your campfire example.

With that said, I’m surprised Apple hasn’t implemented a feature to group/bundle successive photos beneath what is determined to be “best.”

[*] Note: successive photos being separate shutter taps/actuations (potentially several seconds apart), where bursts are continuous (generally as fast as hardware allows, ms apart).