I don't think you're supposed to rationalise how the barbarian designs fit in within IGA's view, because I think he simply ignores it and pretends all Belmonts are nobly dressed Bishies. Kojima Simon is a bit of a compromise in that sense. It's one of the weird side effects of SotN tying all games in one continuity, regardless if it really works. I always prefer to see the two aesthetics as two different takes on the series, and keep them separated.