How many protocols do you know that made that transition at all? I don't know many that even have that level of requirements (low latency, multi-device, low ene

How many protocols do you know that made that transition at all? I don't know many that even have that level of requirements (low latency, multi-device, low energy consumption, federation, scalability) in the first place, and even fewer that managed to pull that feat off. IRC probably has a similar level of requirements, but I haven't heard of its mobile capabilities. Most others seem to be completely new developments and in the case of Matrix e.g. they seem to have solved some issues by reducing the scalability (higher server load). So yes, it took a while for XMPP to solve those issues, and you can say it took too long. But at the same time having done that at all, is an achievement in itself.