Alright, so an update:
I watched TheKengineer's video on the Incarnon Miter, and during the bugs section towards the end of the video, he said that Miter's punch through both does and does not work, seemingly at random.
I tried testing it again, looking at things side-on using Captura's detached camera, and noticed that the sawblades were breaking a fair distance from the enemy they hit, possibly pointing towards some kind of hitbox issue?
When I tested it again in the Simulacrum, I found that punch through does work at certain distances, going through one enemy and breaking on hitting the next. Moving closer to or further away from the target causes the punch through to stop working again, until you enter another sweet spot.
I've recorded another demo vid, using Lavos (to eliminate Slash DoT via status duration, with a 13% duration build), and Eximus (overguard for stagger immunity)