My two main opinions are:
1. This post seems to take for granted that schisms are bad without actually arguing why. Even if it is the case that schisms beget more schisms, that in itself (or that + pointing at Protestantism) is not actually an explanation of why that’s actually bad; it just claims so. It does imply that the badness is in the coordination costs that are increased by a diaspora over a centralised location, but if a diaspora happened in the first place that is strong evidence that whatever central place it spawned from was not only incapable of making this level of coordination happen but also its members judged it was incapable of changing into a place that can do coordination.
2. Two of your main examples are religion and politics, where one can’t really belong to multiple subgroups. For things like the LW diaspora or Discord servers or w/e, schisms aren’t schismatic – one can belong to multiple social groups and Discord servers and what-have-you (which can even be desirable, as you yourself have argued in your post about diversifying your friendship portfolio).