BC pipes and especially diamond pipes are ABSOLUTELY NOT even.
I set up as a test a diamond pipe with 2 cobble on one route and 1 cobble on another. The first 5 cobble through it went to the 1 route so there is no way at all this is anything more than random. And intersections are even worse.
A random chance to hit any side of the pipe will (in the long run) even out the amount of items that go in each direction. Sending 5 items through it is not a significant test at all. With the way you set the pipe up, you'd expect 1/3 of the cobble to go to route 2. 5 items going towards route 2 has a probability of about 13% (2/3 ^ 5). Run a few thousand items through it and if you still have a large deviation from the expected 1:2 ratio, you might have a case