I think the key is blending wort to mitigate the flavor impacts of a 2nd runnings only beer. Blending also removed the big beer/small beer constraints.
Blending preboil is nice because you can produce wildly different beers based on yeast choice, hopping, sugars (think partigyle Trappist beers), etc.
This.
As much as I respect the Fullers method of blending after the boil, I like having the ability to hop each beer individually.