This might be at a tangent, but here goes anyway!
It is often noted that liuhebafaquan (6 harmonies/unities, 8 methods) contains elements of xingyi, bagua, and taiji. However, this point is also often disputed. What I have yet to see argued, and I am putting this out there now, is that the root of LHBF predates the other IMAs and may well have been the precursor to all three.
In the video Josh has put up, and in the approach by yangjia miquan practitioners, there is evident rising and falling. Although this is not so prevalent in the 'standard' 3 IMAs mentioned above, it is a signature element throughout LHBF.
There is no compelling reason, that I can think of, to suggest that LHBF is a composite art rather than the other IMAs being offshoots from it.
Beyond this, while there is much variation in how a body/energy can be moved, there is also a clear indication that the variations are not endless and are naturally constrained by the limitations of physical mechanics. And perhaps the simplest theory is that it is no surprise, given these limitations, that there should be much apparent similarity across arts.
As in the last post, I also want to caution against the type of petty mud-slinging that went on when miquan hove into public view. These videos are indeed very interesting, but they do not cast doubt over the value of existing arts, in my opinion. If they did we would never learn anything properly, as we would flit from one 'newly discoverd form' to another, never settling and never developing. Once again, just my opinion.