Making front-ends to existing back-ends makes a lot of sense to me. I don't really see the advantage of writing a monolithic media player from scratch as opposed to leveraging existing back-ends.
I knew I should have clarified that I don't think it is a bad thing they are "just" front ends to mpv :)
I agree with you that there isn't much (if any) advantage to doing it all again with a new media player core. I would rather all the expertise is put into mpv to be honest and then let others build front ends that do all the extra bits.
