Most Olympic level athletes and high level coaches do incorporate visualization training as part of the regimen.
And, in Japanese training, there is the concept of Mitori Geiko.
As Mr. Moneyberg has not registered a profile here, I have no interest in commenting on his rank.
If Mr. Moneyberg never existed, that would not change the fact, that thoughtful practice, conceptual thinking, and visualization can indeed play a productive role in grapple fu training, and many other types of training.
In fact, in the origin mythology of Gracie Jiu-Jitsu, the story goes that as a teen ager, Helio watched practices that his brothers taught for months or years, implying not active participation prior to that point, until one day, he had to substitute teach a private lesson when one of his older brothers was not available, and that his guard work was seen as innovative by the student.
Now, I am not saying that we should ever take mythologies, or fairy tales, or religious stories literally, but that does not mean that they have nothing to teach.
Nor am I saying that watching practice, or thinking practice, without physical practice, is something that I am advocating in a non-nuanced way.
But, don't throw out babies with bath water.
Thoughtful practice, conceptual thinking, and visualization can indeed play a productive role in grapple fu training, and many other types of training (see, I also like repetitions in training, if you notice the reference).
I remember when I was a white belt I spent a bunch of time daydreaming about BJJ and cooking up ways to transition from my favorite positions into some subs. I went in to the gym and asked a purple belt who had taken me under his wing about them, and he told me I was dreaming. In fact I was, but still felt he must have misunderstood me, since these techniques were totally legit and going to revolutionize my game! I asked if we could drill them out, and he agreed. Once I had shown him what I was trying to do, one of the two he told me to discard entirely, and the other he said had some potential if the opponent was asleep at the switch, but couldn't be relied upon to work against someone who was focused on defending.
So there you have it. 2-3 hours of visualization effort proven to amount to jack squat with five minutes of mat time. But then again, I was just an overeager white belt at the time and now I know that transitions come from a deep familiarity with the techniques on both ends, not daydreaming about how cool it would be if you could connect x to y. I'm sure Mr. Moneyberg in his purple and brown wisdom found ways to get beyond that limitation.