proxy media and full resolution media must have matching audio channels

Yes - this workflow makes no intuitive sense to end users. The whole point of proxies is that you're linking two video files with completely different settings. Audio should not get in the way of this linking, just like video currently doesn't get in the way. The error message that pops up when attempting to attach full resolution media to files with mismatched audio ... imagine if that error message also said "the video settings don't match." The user is going to think "duh, that's why this whole workflow exists, so I can link media with different settings."

Following that logic, this is a giant design flaw in Premiere that breaks one of its most useful features for editors.

This is a total pain in the butt.