I’d love to be able to disagree in any of your points, but I can’t.
The vast majority of users want something that simply works, is polished and intuitively usable. Reading docs, remembering anything other than the bare minimum, running into issues that don’t get magically resolved within 5 minutes will turn them away forever.
Even people with a technical background will at least partially compromise and migrate towards the services with the most users to not isolate themselfs.
Matrix is neat, Lemmy is neat, Nextcloud is neat (well, in theory), Immich is neat, so many other privacy friendly solutions are neat. But they’ll always be irrelevant in the global context.
Selfhosted services like Nextcloud/Immich aren’t nearly as dependent on a critical user mass like Discord/Matrix, but the principle is the same.
If you host for family or friends, they may even use it if you convince them to switch. But when the setup, which doesn’t consist of redundant instances and isn’t maintained by a small army of SysAdmins 24/7, inevitably breaks for longer than a few minutes, most will switch back to the easy, reliable option.