I'm not sure who is pushing #GlobalSwitchDay probably won't amount to anything, some of these platforms are certainly not ready a massive migration. The #RedditMigration was rough enough on Lemmy, it actually murdered #Kbin; #loops #PeerTube and #Friendica don't have nearly enough well-maintained instances to support any sort of massive migration. And Signal, well its better than WhatsApp, and its mostly Free Software, but it doesn't really align with all of the others that are, or at least intend to be in the case of Loops, federated services based on ActivityPub.
I agree with your points. I'd much rather a decentralized solution would pop up that would be easy to onboard "normies".
As outlined in this mastodon thread, you can see a few pain points mentioned, a solution offered, but then there's a glitch in fluffy chat that doesn't allow for uName/PW sign up.
Decentralized alternatives are great in theory, but in order to gain the critical mass of users needed for a successful migration, there needs to be a happy middle that results in better/easier UX. Mastodon is much more fleshed out than matrix in this regard IMO as you don't need to deal with key mgmt, yet you still see users migrating to a less mature platform, Bluesky.
Dessalines also has a good write up on a few of the other alternatives here. https://dessalines.github.io/essays/why_not_signal.html#abandonment-of-open-source
Matrix, however, also exposes metadata that can be used to link who is talking to who
GNUNet seems promising