trick question, 239.9?
i'll bite though and say 239.9 would not apply, sorry, couldnt resist.
#2 Cu works for the 125a dwelling feeder from 310-15b6, and when you say "connected as if a bc" i assume you mean its installed on the stabs in the mlo panel vs using a breaker kit at the main lugs???? which is ok too. so was wondering if you were getting at 230-71 six switch rule which wouldnt apply to the panel setup you described, or maybe 384-16g because your feeders are backfed to this 125a breaker instead of to a main lug breaker kit, so you have to be sure to use the additional fastener on that backfed 125a main disconnect, right?
so i give up if its something else you were fishing for, but thought i'd try these. -C-