My proof is various places that Ive heard this from and personal experience: Youtube golf pros, PGA pros that Ive taken lessons from, golf magazines and golf instruction shows on TGC. Ive played with all 3 grips from time to time and find that my wrist action is most passive with the interlock.
Thanks. Confirmed what I thought. :)
I'm sure you'd agree that what you've offered is not really proof at all. It's a personal experience combined with "hearsay" from others. It's exactly the kind of situation that had most golfers thinking that the ball starts in the direction of the club's path for decades.
Furthermore, "passive" wrist action might very well be a good thing for a golfer…