So... I have a Samsung Galaxy Watch 3. And it's still chugging along. Biggest fitness use for me is sleep tracking, O2 tracking (during sleep), HR tracking (during sleep) because I have a low resting heart rate so I have to keep an eye on shit. Nice but not required to be able to see message notifications on it.
I have yet to see any compelling technical reason to upgrade. At most the newer ones also do skin temp, but that doesn't seem like some big must have fitness watch feature.
I've heard that eventually they're working on blood sugar monitoring (which would be good for my mom), and blood pressure, although I have no clue from a tech standpoint how they'll ever do that. But of the current fitness watches, is there really a compelling reason to upgrade?