This isn't sustainable open source development in any practical sense. Sure, it's technically open source, but nearly useless for anything but consumption straight from Google. I'd say that that makes it practically not open source.
And it's kinda my whole point: code that can only be consumed wholesale as shipped might technically be open source, but if backporting fixes to a year old version is nigh on impossible, is it truly open source in practice?
Debian has a release model for a reason and it's their raison d'etre. Of course they don't want to compromise that.
Considering the amount of other distros that use them as a base they're providing something that people want.