PianoMonk I'm glad you (and many others) find Molly's info useful. I feel differently and think her "generosity" is, like so many other YouTube music tutors, gurus, teachers, experts, ultimately money-driven.
I don't think there's anything inherently wrong with that. Yes, it is a marketing strategy to put out free information and then have more detailed information behind a paywall, but it still helps a lot of people who don't access the paid content, so kind of a win-win.
I'm skeptical of "new" approaches to methods that have worked for so many in the past, especially with something like music. To me, learning to play a musical instrument isn't rocket science, or even neuroscience. The process is simple - you develop technical aspects, study the theory, and work at it.
Well, what makes you think rocket science and neuroscience are any different? Develop technical aspects, study the theory, work at it is how you develop any skill. So, the statement is not that useful.
If someone wants to learn to play a musical instrument, they should seek out other players of that instrument, ask them what they did to get where they are, and find a teacher (a live, in person, beside them on the bench teacher) who understands the path the student wants to take, whether it's wanting to play jazz, classical, or just play Christmas songs when the family gathers, and practice, and study, and play. That's it in a nutshell.
The problem is that not all players are good coaches, and even the ones who are don't work for everyone.
However, some students, no matter how much they practice, no matter how they practice, no matter how long they practice, no matter how many books they read, or how many YouTube gurus they subscribe to, will never reach the level to which they aspire. In my thirties, I gave guitar lessons for several years, mainly to young guys who wanted to play in a band and make lots of money. Sadly, for some of those students, it was clear to me, right from the start, that the most money they would make from their guitars would be the day they sold them.
There are still more effective and less effective ways to practice, many of which are not obvious. Molly Gebrian condenses a lot of useful information well. You are merely saying that talent and the age at which you start play a major role. But that isn't a counterargument to the role of practice/deliberate practice.