Custom protocol handlers would be cool if they're built into every browser, and they always work. But that's a dependency that's brittle, and breaks too easily.
FB wins b/c they have one coherent system that all works together. The Fediverse loses b/c it requires far too much technical knowledge. That's the bottom line of Tim's posts.
So, keep up the fight for custom protocols. But let's also do the things we can *right now* that don't wait for Apple, Google, and Microsoft.