The separate components of Jitsi make it quite clean to scale and customise though. A monolith doesn't seem superior except for the very smallest deployments where simplicity is key.
True. Galene is designed to encourage small deployments: it's a single binary that is simple enough and cheap enough so that every high school can have their own instance and not rely on an external IT team.
For large deployments, where accidental complexity is not as much of an issue, you'd most probably want to use some more complex and more flexible software.