I see exactly what you are talking about buckeye and I agree you will have some of the vane on a helical fletch pass through the black bristles. However the rest of the arrow is still being supported by the other bristles and while the black bristles are stiffer they are not that different to where you get an erratic arrow flight.
Not exactly the point I was trying to make....
Go nock a helical arrow on your bowstring... Slowly pull the arrow thru the WB and let me know what the vanes do, especially the hen vanes....
My problem with shooting a helical fletch thru the wb is the fletching is commited to it's path as the leading edge of the vane dictates where it "cuts" thru the bristles at..... The back end of the fletching is in for a ruff ride.
IMO I would not shoota helical arrow thru a wb.... I have used a wb in the past as well, so I am not a hater... I am only saying that it has it's limitations.