The parent post says "the only viable instance" which implicitly packs an assumption of Mastodon-like topology: a single product is expected to be split into many "instances", with some of them being more or less "viable", and that a lack of many "viable" "instances" is perceived as the protocol not being a real thing, or failing to live up to its promise. (How else are you reading "viable instance"?)
I believe that if you look at the network topology, this argument becomes much closer to "Google Reader being the only viable instance of Google Reader means RSS is a scam with a single player". Which is an absurd thing to say. That is what I'm trying to show by picking at the word "instance".
Do you find my argument flawed, or just the way I present it? How do you prefer I present it alternatively? And how do you read the parent post? My issue isn't with the word, but with the implication in the parent post.