I agree with all that you have written. I have found the BE agents to be conscientious with trying to figure out why an Advantage booking is working when a BE booking is not.
They were the ones that said that a single connection to a "gateway city" would work, but two connections would not. So..... MDT-CLT-PHL-LHR would not work, because the CLT-PHL segment was invalid for a BE award. However, MDT-PHL-LHR would work.
So, the BE agents were helpful. However, I would appreciate better transparency for how to construct awards on BE.