For APFS, I don't buy that it has anything to do with prioritizing one operating system or the other. APFS wasn't ready when Sierra was released, which is why it was included as a beta with limited functionality. It seems to be ready now, so it will be included in the next version of iOS (10.3), which is still in beta, and presumably the next major release of macOS.
The only difference is that it's being released in a minor update to iOS but will probably wait for a major update to macOS. But that makes sense, because macOS allows the user to customize partitions and filesystems, and allows running other operating systems - including Boot Camp, which Apple itself must provide drivers for, and Linux, which is waiting on Apple releasing documentation for their filesystem, as they have promised to do. By contrast, iOS has the same partition layout on every single device and no cross-OS compatibility concerns. Thus APFS on macOS requires more work and has greater risk of failure. For both reasons, regardless of Apple's priorities, it would be logical to start with iOS. Even if Apple did add stable APFS support to a minor macOS update, they probably want to auto-convert users to APFS eventually, but doing so in a minor update would definitely piss off technical users; they could make it opt-in to start with, but it's easier to just wait.
The next version of macOS is only a few months away; really not a big deal.
(I agree that Apple seems to be prioritizing iOS in some areas; I just don't think APFS is one of them.)