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I've always used a proper garmin for strava-ing so can't comment on that bit.
I've apple-watched in tandem with power meter to compare calorie burn and it seems close enough that for commutes/ general bike messing about/rides where either using a garmin or garmin/hr combo is a faff I'm happy to let the watch take the strain.
For general activity (running about, walks, etc) it seems very good at catching anything over baseline, as well as logging general through-the-day HR (not constant, spot readings only). Plus the daily goal thing has provided some activity prompts during my more sedentary wfh days.
I've got my Strava plugging into Healthkit along with daily step counts/activity burn from the watch etc, which then feeds into Myfitnesspal to tell me to eat more/less, and it's a system I'm happy with. Plus the watch is still providing novelty for phone notifications etc, and the mfp app provides an on-watch 'how many calories left for the day' number so its one less thing to stare at the phone for.
All in all, a very expensive tool but no regrets. If you're not already heavily invested the ecosystem probably not worth it.
@tricitybendix has had one since xmas had has just finished a unbroken month-long activity streak so is probably better qualified to comment on how it does everything really.
fitbit not talking to apple health was a dealbreaker for me when looking for a wearable to purchase. was considering the microsoft band (2) as it seemed a bit happier syncing, had on-board gps as well as the hr doodad, but in the end went for an apple watch. ho hum. no complaints with it really, but it feels like overkill for a fitness band and underkill for anything else.