As your data and that of others show the two clusters have similar apparent and absolute magnitudes (M10 is slightly brighter), very similar distances, and M10 has only a slightly larger radius. However, I had the distinct impression of resolving many more stars in M10 (a larger instrument or camera would have resolved more in both). This observation seems consistent with the data that suggests that M10 is twice as massive as M12 and therefore has many more stars on the RGB spread out over a slightly larger area that allowed me to see them fleetingly.
It’s unfortunate that your observations of these two clusters were done with very different equipment. Perhaps you will revisit them some day.
Edited by Organic Astrochemist, 13 August 2022 - 04:13 PM.