I think the other thing they do is decrease the image quality when multiple people are simultaneously connected. This is a nice hack since you don't really notice the difference, and users blame bad images on the network not the product.
The biggest challenge to their business IMO is if/when WebRTC becomes stable between all browsers. There are still many kinks that need to be worked out. Everything falls apart in the P2P version when you have more than like 5 people connected as the amount of information that needs to be transferred across the network scales exponentially.[0] So you need to add a gateway and connect everyone over a single pipe.
more details - https://webrtchacks.com/zoom-avoids-using-webrtc/
That's the great thing. There might be an entire market of options out there for an idea, but if they don't get something like reliability right, then that's the easiest foot in the door.