qt5 is still needed by … vlc so its kinda circular that way at the moment.
As to phonon-qt5-gstreamer … arguably it shouldnt have been the choice in the first place, and you can choose to replace it with the vlc variant, but there is no requirement to do so.
Eventually I would expect to remove that package altogether.
And … I tried, as phonon-qt5-{gstreamer,vlc} and phonon-qt5 only depend on eachother and are not required by anything else.
But upon a reboot smplayer could not play videos, and could again after a reinstall.
(which sorta makes sense as it still depends on qt5…)
PS. For other smplayer+wayland users … make sure to check Wayland support under the video tab in options. 