Yes, their proprietary scalable video codec is what makes the difference.

It's miles ahead any competition and pretty much the only tool which will give you decent calling experience on spotty connections.

Before zoom I was mostly doing audio calls on a computer, with zoom video is easily manageable (actually, not sure if that's a plus for society, it certainly increased the meetings / productiveTime ratio).

True but I believe Skype P2P mechanism is dead end on current computing environment. Few companies like Microsoft can host servers for such free services.