RTSP is a simple signaling protocol which they cannot replace with anything for many years already, and it has to be admitted that they don't try really hard.
For example, we have an IP camera that supports RTSP. Anyone who has ever tested the traffic with a Sharkwire cable will tell you that first there comes DESCRIBE, then PLAY, and then the traffic begins to pour directly via RTP or wrapped in the TCP channel for instance.
There exist two main functions of WebRTC operation on the server side in the field of streaming video: publishing and playing. In the case of publishing, the video stream is captured from the web camera and moves from the browser to the server. In the case of playing, the stream moves in the opposite direction, from the server to the browser, is decoded and played in the browser’s HTML5 <video> element on the device’s screen.