I don't buy these rationalizations at all. As was previously said, HLSe has been using fragment level encryption for many years, with AVC and MP4, so we know its possible. This is not theoretical. https://paramountplus.com and https://cbc.ca
and others use HLSe on some streams currently. You don't need box level encryption, and requiring it just add pointless MP4 parsing and overhead.
They're not rationalizations. They're implementation choices under legal, engineering and product constraints. In particular, Paramount and CBC allow themselves to use HLS encryption forbidden under typical content protection contracts.
