Media session notification being bumped to front even when not in use

You are mixing things, notifications and media sessions are fully unrelated.

You can easily hide all the notifications that only says Symfonium, they are required by Google but useless

For the media session your device kills Symfonium and restart it, so the paused media session is updated, but it’s never active, so can’t be pushed as first else music would stop on the other apps.