The problem that I have with this section is that there is nothing in the definition of "main power feeder" that requires this feeder to supply the main power to the dwelling unit. There is nothing about the diversity of the load. The wording only requires one thing: that the feeder be between the main disconnect and the lighting and appliance branch circuit panels. It doesn't even say that this feeder must be directly between the main disconnect and the lighting and appliance branch circuit panels. If you just apply the words as written, then all feeders within the dwelling unit are "main power feeders". This is very poor code writing. Yes, the intent was that these feeders are required to provide the main power to the dwelling unit, but it is not easy to enforce intent. The inspector can only enforce what is written in the code book and the words as written permit all feeders that feed lighting and appliance branch circuit panels to the sized per Table 310.15(B)(6).
Don
