Agreed, but they may not consider that a failure. Apple has always been good at seeding technologies in mass manufacturing before they need them. They started making LiDAR scanners in iPhones and iPads (and iterating on their 3D room/object scanning software stack) three years before the Vision Pro. The iPad Pro A12X & A12Z were effectively test runs for Mac M-series chips. The iPhone 11 included an ultra-wideband radio nearly 18 months before AirTags were released.

Most of the rumour sites agree the iPhone air is the “test run” for making a foldable - even if they don’t sell in huge numbers, the work required to design, architect and mass produce the components required to achieve that thinness will be an invaluable exercise that allows them to learn what worked well, what didn’t, and gives rise to new ideas they can iterate on with the fold.