The artifact is caused by packet lost with RTSP. Can you use larger “latency”(the default value is 2000 but you use 150 and disable “drop-on-latency”? And there are many quality related properties of rtspsrc, you can try to tune them. rtspsrc
uridecodebin works better and slower is because it will setup a RTP session and use rtpjitterbuffer to maintain the packets.
https://gstreamer.freedesktop.org/documentation/additional/rtp.html
There are a lot of resources for gstreamer RTSP, you can google it.