Mastodon, Misskey, Lemmy, Pixelfed are all very different, with different feature sets, supporting the same basic protocols, and evidence you can build something new on distributed protocols.
ActivityPub dictates how to meditate relationships between activities on collections of objects, and a few default objects types. It's specifically designed to let you "subclass" (not really inheritance, and more composition as you give a list of types with no enforced hierarchy) objects so you can create new object types nobody else understands but still give them another type that allows them to carry out basic operations on it.
It's not perfect but it's far from as dire as you make out.
ActivityPub dictates how to meditate relationships between activities on collections of objects, and a few default objects types. It's specifically designed to let you "subclass" (not really inheritance, and more composition as you give a list of types with no enforced hierarchy) objects so you can create new object types nobody else understands but still give them another type that allows them to carry out basic operations on it.
It's not perfect but it's far from as dire as you make out.