Signal's own official clients failed to properly back off from spamming the server with incessant requests. I'm not entirely sure how more third party clients would have helped with this issue.
Realistically, I understand that the Matrix.org homeserver is an enormous part of the network and an outage there would be comparable to this one.
However I believe that to be an orthogonal problem that also should be solved.
I'm actually curious, why does Matrix promote the Matrix.org homeserver so strongly? Why isn't there an easy link to community-run homeservers?
If you look at Mastodon for example [0], their onboarding process directs you to a registry of community servers [1], which actively promotes diversity in the network and therefore network resilience and reliability.
Matrix meanwhile, just links you to element.io, which creates an account on the matrix.org homeserver.
The web broke. We just have wait a bit while the Elders of the Internet sort this one out."
Said no one ever.
Synapse (Matrix reference server implementation) had for a long time severe performance issues when dealing with large rooms. Clients would try to enter a room and would take literally forever to be able to get messages for that room.
Also, the natural reaction from people upon seeing how some rooms from bigger instances were causing problem was to create their own instances and their own rooms.
Federated protocols are anti-fragile.