You don't need to transfer music if you're using Google Play Music (including the option to upload your own music), Spotify (has a similar options), or something else like that.
I'll give you application settings, but that's only because the applications didn't bother implementing the backup services.
I get it's easier, but that's not the point here.
It looks like Google either doesn't care or deliberately cripples experience for users who don't go all-in on all their services (given that Maps explicitly refuses to save recent searches locally I'm think it's the latter).
I've migrated from Nexus 4 to 5 and it was a mess (Google Play is full of dodgy and incomplete 3rd party backup apps. Android File Transfer is slow and leaves partial copies behind when any error happens, and errors happen often, etc.)
I could see your point when it comes to privacy, but the photos are still available locally as well. By the time you're replacing phone the photos will probably only be used for archival anyway.
Case in point it took me a month to upload my music to iTunes Match (and it already has fingerprinting).
Simple read access to the contents of an Android device was always one of the big "pluses" in my experience. Then if you find that too difficult for whatever reason, there are Google apps that do the same thing. The only bits that can be annoying are app settings as you mentioned. Even that has improved and I notice a lot of that stuff showing up when I sign into a new device. Still, I hope to see some improvement on that front in the future. Third party migration apps (like the one on my Moto X) can do it so Google should definitely offer something similar. It currently works for some settings/data but I'd hope they're working on adding support for more.
Automatic app settings backup (to google drive) is finally coming to Android M [0]. Third party solutions have existed more or less forever, though the best ones require root. For the local music/photos stuff, is it really that hard to plug both phones into a computer and transfer stuff that way? It would take maybe an hour.
[0] http://arstechnica.com/gadgets/2015/05/android-m-makes-anoth...
Google only copies system settings and list of installed apps, but not "sd card" data with local music, photos, apps' settings or data.