I think you and eli are both right. Neither Gab not Voat are likely to succeed, because of network effects.

The only way a new social network is likely to succeed is if it is part of a federation of social networks that communicate using protocols such as ActivityPub, making one big network where the whole exceeds the sum of thew parts.

Sure, but mostly because they’re full of exactly the sort of people I don’t want to interact with

That may well be true. But maybe some Gab people want to interact with some Voat people, and if the applications were interoperable they would be able to.

And I am sure dig was not worried about Reddit... and MySpace was not worried about Facebook, and AltaVista was not worried about Google....

The idea that Reddit, Twitter and Patreon can not be supplanted show an ignorance of history

They're not going to be supplanted by platforms that cater to marginal viewpoints. Gab and Voat, almost definitionally, cannot achieve mainstream success.