Not sure it's worth debating this in much detail because wl.com is what it is, but FWIW:
I liaised with Davis when they first rolled out the upgrade to WeatherLink.
1. The ported the original design which was based on a device ID to become an account_device.
Yes, a device is a single upload_device which is effectively a station. Not sure what else Davis could easily have done that would work across their whole range of station types including EM and WLL as well as traditional loggers. (Though no doubt other architectures are conceivable)
2. They didn’t allow user account management to delete a device.
True. But admin accounts can delete devices, though these accounts aren't available to end-users.
3. This was a transformation and they had the chance to fully normalise the whole structure to allow the export/transform/load (ETK) to completely manage any variation.
It was a big project to move to wl.com v2 and some limits to the functionality available to end-users was necessary (and possibly prudent too). Again, admin accounts have pretty much full control over user accounts.
4. A station is not based on a transmitting device but location and station
See [1]. (I presume that by 'transmitting device' you mean an upload device?) Location is a valid search term for a station but it's not part of the station's identity.
5. A device can fail, so it must be able to be replaced, this applies to all variations.
As indeed it can be, but by an admin account.