I think you may be underestimating the amount of people who would buy the easy sollution. I've been part of a makerspace where we've tinkered with 3D printers since before it was cool. I still have a Bambu Lab printer myself because it's the "iPhone" of 3D printers that just works out of the box. I used to have a Linux laptop and now I have a MacBook because it's easy.
If I were to buy a NAS it'd be the "iPhone" NAS because it was easy. Though I don't think your prediction for Synology is wrong. I'd certainly pick the one that didn't previously try to push their own HDD's.
It is also competing for simple solutions like an old mac mini and DAS. Now that would truly be an "iphone" like experience for someone already in the mac ecosystem since time machine lets you choose another mac on LAN as a backup endpoint with little fuss, and now you can make use of Airdrop for mobile devices. AFAIK backing up to a linux box is not nearly so trivial at least with still using Time Machine.
If I were to buy a NAS it'd be the "iPhone" NAS because it was easy. Though I don't think your prediction for Synology is wrong. I'd certainly pick the one that didn't previously try to push their own HDD's.