A mixture of NixOS and Debian, depending on the machine. NixOS is trivial to maintain and to keep predictable and tidy. When its weirdness is a problem, Debian is my answer. It doesn't get more normal than Debian.
If you're asking about a personal opinion: any policy purely based on tradition is worthless. Tradition is just peer pressure from dead people. Just like any peer pressure, it's highly unlikely to produce anything but grief. If something is based purely on tradition without any other reason to exist, it's unlikely to be an optimal policy.
Back to the initial question. I don't think we can get infinitely progressive but we can keep subtracting the cruft of tradition until there is no necromantic peer pressure left at all. Mind that if something happens to be a tradition but still has a good reason to exist, it should be evaluated like any other idea in terms of being good or bad. I mean removing just one of the reasons to keep this idea. If it is left with zero reasons, it's out. Otherwise it's fair game.
It doesn't use the system libraries, unless the system in question is NixOS. It still provides its own dependencies. Arguably in a more elegant and less wasteful manner, but they are still distinct from the ones used by the rest of the system.
In terms of the memory usage, it's a reasonable approach these days. It gets hairy when we consider security vulnerabilities. It's far easier to patch one system-wide shared library than to hunt down every single application still bundling a vulnerable version.
It certainly feels dangerous if forced upon users not aware of the trade-offs. For people already accustomed to using hardware keys, it's very much an improvement, as more services will support them too. The problem is in the awareness. On the other hand, people already treat regular passwords as throwaway data and expect services to just let them in, or even never log them out. In this scenario, maybe passkeys can still be an improvement: roughly just as much as enforcing using a password manager.
Federation combined with keeping the historical federated data consistent is certainly a bitch. We can't have it all. It could be like email that only handles delivery at any point in time and history is purely local, but Mastodon specifically keeps the federated data public. Propagating the change on the historical data to the federated instances would be nearly impossible. I don't see how it could have been done better without sacrificing something else.
I don't think they could do anything about it. As far as I know, Mastodon doesn't support any kind of instance renaming, so the hostname is one thing you cannot change. You can only spin up a completely new instance.
I'm pretty sure "SSG" isn't a part of his name.