TrueUp https://www.garmin.com/en-US/blog/fitness/garmin-connect-updates/ favors higher quality devices when calculating calorie burner a particular activity (good) but still double counts due to calories burned due to daily steps. Simple repeat by:
record a run with the device which is your activity monitor
continue normal activities for the rest of the day
You will see that the number of calories attributed to "Daily Steps" INCLUDES the run that was logs. This means that the run is being double counted which can significant effect accuracy of calories burned in you did a long run.
Just as a higher accuracy device should take precedence over a less accurate device, a logged activity should take precedence over general activity tracking.
NOTE: This issue over been raised in numerous topic areas since 2015. It would be great to get this fixed.