It still has the issue that joining a popular channel can bury a server for a couple of hours whilst it downloads the entire history since it was created (hillariously trying to connect to thousands of servers that no longer exist… the error log was… impressive).
The new protocol was announced on here recently but synapse is stull running the old protocol with a proxy in front and the proxy just means clients can log off whilst it’s updating, it doesn’t fix the issue.
It’s probably fine if you don’t federate it, but I could just use my IRC server for that…