Don, I can't find photos in Brister's book to support my point, but I think Brister shot enough targets to have detected a difference in how full performs (in terms of how rapidly it opens) compared to IC (or chokes more open than that). Here's a quote from his book:

"The full choke's reign of superiority is considerably shorter in useful yards than IC's . . . By 55 yards, with ordinary hunting loads, the full choke has become less efficient than the IC as 40 . . . So what we have here is one choke that is quite deadly for a distance of about 18 yards (from 20 to about 38 with most hunting loads in a 12 gauge) and another that shines for 10 yards or so with the same ordinary load."

This is from a man who was more than capable of using a full choke at long range. So it's not as if he didn't understand full's advantages, for those who shoot well enough to benefit from them.