They still should've handled it differently. Show a warning to the user encouraging them to migrate, give a reasonable window before the feature is actually disabled, and don't let the users upgrade to a version which will break their storage.

Synology made a mistake which they admit:

> DSM incorrectly allowed administrators to migrate from a BTRFS-capable device and utilize previously created BTRFS volumes on the affected devices

And they're punishing users for it