The issue is mostly due to the nature of the mobile IP, rather than inherent WebRTC variables.

However, ORTC does seek to improve with simulcast/SVC, and attributes of ORTC will merge into WebRTC as well, ultimately providing more hooks, finer-grained control and better instrumentation/visibility to the upper layers.

All that said, you can do acceptable quality WebRTC voice and video over 4G LTE today. But you do need a rock solid signal and be prepared to with a fully charged battery if you are not plugged in.