I definitely agree we should have more granularity when it comes to the settings. LG was *so* great about giving us an absolutely obscene amount of it in our video settings, but I can't turn off the irritating "no input detected" pop-up, modify the screensaver in any way or even change the rotating wallpaper. I mean, that's BASIC customization, and ridiculously easy to implement.
I don't know anything about Deezer, but it seems odd that the changing subtitles wouldn't be enough to untrigger the screensaver. Conversely, I find it frustrating that the screensaver doesn't work with external components like either of my Playstations, my 4K disc player or my Chromecast. It doesn't kick in at all. If it's *that* critical, LG (and I personally agree that it is), then the input choice shouldn't matter. If you have something like that, maybe try accessing Deezer through it instead of directly through the TV?