The story goes:
Jimmy Demaret was playing golf with Ben Hogan, one day, shortly after the 'Fundamentals' was published. Hogan made a poor shot, yes, out-to-in, Demaret asked if he heard the glass breaking.
This comment was from a close friend, not an enemy, and demonstrates, the stand-offishness among pros about swing plane concepts. To mix a metaphor - many ways to skin a cat.
Remember Trevino's arched left wrist at the top, and many other very good ball strikers who were not conventional.
When Brian made his comment about Ping and Henry Griffitts, he was obliquely referring, I think, to how the club is soled and the consequent shaft angle at address.
All these great & very good ball strikers return the club to the address plane (or very very close to) at contact - ie the way the club was designed. It is not of absolute importance of how it got there.
Some people may be able to, and need to, have the plane & the club theoretically perfect at the top - pointing parallel to the target line. I like many others have no concern with this.
Good teachers like Brian know & teach the swing around-ward, a swing with depth. Faldo talks about the concept of the late-hit being really about the club lagging behind you, or your hands. It's late getting there. He also teaches the right wrist turned back on itself, as Brian does, this also encourages a deep circularity in the swing as opposed to a shallow around and up swing. All this promotes an inside path to the ball and militates against the swing getting too steep.