Really has nothing to do with 'Default', you can have several players in the sound menu,they'd be listed top down in order of install/activating, in other words the order listed in com.canonical.indicators.sound - interested-media-players which can be adjusted as desired.
Atm there are at least 3 specifically enabled - banshee, rhythmbox, clementine, additionally vlc-1.2+ has MPRIS2 support & works to some extent.
From my perspective the 'quality' of sound menu support is best in banshee closely followed by clementine & rhythmbox. Banshee & clementine seem to lack album art in the menu. (I not sure if guayadeque has or will have support
Vlc works ok, has album art but as it wasn't specifically coded for the sound menu it can't be minimised to it, only opened & controlled from it.
There is some interest possibly for audacious but nothing yet.
Unless you or someone else is up to the task of adding MPRIS2 & then enabling as intended for the sound menu then yes, you are "dependent on the developers of the music players.." not only for MPRIS2 but also proper integration into the menu.
screen example -