Think of Apple Health as more like the Photos app on iOS than an online service like Garmin Connect or Google Fit or something like that.
Apple Health data are only stored on your device unless you choose to synchronize them to iCloud, in which case they're e2e encrypted.
Apple does occasionally offer the option to contribute to research studies, in which case they'd have access to the relevant data but this is an explicit opt-in.
All the Apple Health data are also available through HealthKit APIs so that they can be used in other apps, including various export apps (though export is also a native feature). Use of this API requires an explicit app-specific and data category-specific opt-in from the user.
All this is to say: I don't think it's accurate to say Apple owns your data in this case. Apple likes to put themselves as privacy-first and you may disagree more generally whether they live up to their image but IMO this is one of the cases where they've done a pretty good job.
