Well I think I figured it out. The answer makes me sound dumb but I’ll go ahead and share in order to put a nice closing on this conversation. For some reason, the “Make Self Contained Movie” box was unchecked in the Export QuickTime Movie dialogue. Now, it was my impression that this box should always stay checked unless you want to make a reference movie. It was also my impression that reference movies won’t play at all (as in, not even a distortion and looping on YouTube) when they’re disconnected from the source files.
But checking Make Self Contained Movie cleared it right up. Now to test whether the compressor settings you have pointed me toward make for a better upload…