A decentralized developer community is resilient against this sort of attack for the very reason GitHub is so vulnerable: size.
No, it’s not. Not in literally any way. Not 1%. Not 0.000000000000000001%. You don’t even get security by obscurity as a nebulous benefit because the core mechanisms are basically the same between instances.
No projects are being compromised. They’re being imitated and passed off as the real thing to the naive. You can just as easily do that on another server (including established ones by adding multiple domains to your scripts) when people expect to use thousands of different git hosts as you can on GitHub, except without the benefit of the scale of Microsoft’s expertise at handling this type of attack.
I’m all for federated git being the way forward. I’d love to see it grow into a reasonable option. But it has no benefit in any context against an attack like this.