I think Apple will be happy to leave the Prosumers behind and appeal to people who are less active, and maybe even be a first step towards dedicated sports watches. At least for now.
After a year with the Apple Watch as my day-to-day watch and Garmin Fenix 3 for sports (swim, bike, run, hike), I've now switched to Garmin Forerunner 235 for day-to-day and Fenix 3 for sport purely so I can get all of my data into a single repository, easily.
The one killer app I'm missing on the Apple Watch is Siri.
Agree -- I love my FR235, but Siri is the only feature that makes me want an Apple Watch. On balance, I still prefer my Garmin, though.
You clearly haven't used the watch or any HealthKit related apps. All of the data collected in any HealthKit app or accessory is available to all of the others. Strava knows if I ran using Nike Run Club yesterday, Withings knows that I biked with my Wahoo cadence counter over the weekend, and my diet tracker knows how much I weigh from my Withings scale. There is no lock-in such as you describe, it's incredibly open, portable, and under my control.
I get 5+ days of battery including two 35+ minute GPS tracked sessions, and permanent 1-second update HR tracking all day.
The only improvement I'd like is if it was about 3mm slimmer, so it would fit under my shirt cuffs a bit better ;)