After just watching the video clip of Charlie Mller at Glenn Bishops website. I noticed he dealt seconds from a full grip (four fingers all on the sides).

Did he do all his deals, including bottoms, from a full grip?

In the Busby Book The Man Who Was Erdnase or perhaps that book should be called the man who may be Erdnase - they talk about Charlie Miller being able to switch the grip from the grip that he used to an Erdnase grip while dealing bottoms.

This is also talked about I think in the Revelations video by Vernon.

I think that Charlie Miller used whatever grip he wanted to for whatever deal he decided to do. One grip is no better than another if it gets the job done. A magician can strike second for many different grips.