Those issues are typically from the decoding libraries you choose. Which could even be ffmpeg if you wish. GStreamer just provides a nice high level API.
It doesn’t mean anything for desktop users, it’s just a new standard that could have wider support than VAAPI since it’s part of Vulkan. Mostly embedded devices lacking VAAPI support today, though nvidia requires a third party implementation so this might improve that situation.
This oversimplifies reality. Fedora has a community and actively makes decisions RHEL has no interest in. But yes they also help with testing many things.