I don't see how you figure that. if the NEC rules apply, it does not matter if the thing is UL listed or not. You would have to apply the rules. You don't get to ignore applicable NEC rules just because something is listed.
Sorry, but yes you do, to a point. If a panel is UL listed, an inspector does NOT have to go through the entire panel. There are differences in the rules for UL and the NEC, but if a panel is already listed, it is thereby acceptable per the NEC. If there is a mistake inside, that's a different matter. But I have been challenged by installing contractors on wire sizing inside of a control panel many many times based on the NEC, but the UL rules are different and prevail INSIDE the listed panel. I have never lost one of those challenges, AHJs always agree.
IMO, if the NEC rules do not apply inside a listed piece of equipment, they don't apply inside the same piece of equipment that does not have the listing sticker on it.
I'm not too sure about that either. If you are in a part of the country that does not require NRTL listing of control panels, I don't think an inspector is going to ignore things just because it is enclosed. Conversely if you are in a state that DOES require NRTL listing, an unlisted control panel could (would) be rejected regardless of passing NEC muster or not just because it s not NRTL listed.
Having said that, we build some UL listed stuff with this exact problem and to avoid having this argument in the field, we avoid the problem. It is a little wierd to see a #6 come to a fuse block from the distribution block and see #16 come out of the fuse block.
There is never a problem with over sizing conductors, so your method is never going to be wrong. I just don't accept it as necessary and have never done it, and never had a complaint about it either.
Open ANY manufactured starter or MCC bucket and the wire feeding the primary of the CPT is never over 12ga, usually 14ga (because that's the minimum per UL). That's because all UL says is that ungrounded conductors must have over current protection IN them. In the case of a tapped conductor situation, if the branch protective device is already the right size you don't need it again but if not, you do. So in the case of a starter for a larger motor, the BCP will end up too big and you must have new BCP devices IN the conductors; the primary CPT fuses satisfy that condition. It doesn't matter that the fuses are at the other end of the wire, as long as they are there. Again, AS LONG AS THE CONDUCTORS DON'T LEAVE THE BOX.
I think we may have to respectfully disagree on this one. There is nothing WRONG with over sizing the conductors, if you can, but I don't agree with the necessity.