I agree that talent is not enough, the necessary time, the proverbial ten thousand hours to master a craft is necessary. I say that people with talent that do not work don't "get there" and people with little talent who spend the time working yes. But "there" is a very different place for each person. The best one person can get in art is different than the best others can get, and there are big gaps "there".
When you say "The “visualization” skill you mention is not an innate and mysterious talent: it´s the result of all the hours, days and years spent looking and drawing". I don't say "mysterious". I say that people usually don't focus on that ability because is something we can't describe, untangled from the mix (like for example we can say" you are good t composition but have to work in anatomy), or simply understand. And perhaps is developed a little through years of drawing indirectly the same way if you spent your life working as a docker sure you are growing some muscles but not even close as if you go to a gym with a proper and specific training. And the specific training for that important ability is not drawing.
Because people with this talent draw without difficulty, they draw a lot and continue drawing because they have results and have fun. I don't say it can't develop a little the more you draw, but I don't see significant changes on artists. Good artists were good from the start and "bad" artists were "bad" from the start.
We all are different, and this is a talent much more important for an artist than rules because rules are easy to learn and don't make a big difference, and yes, some people just have it, or I think that more exactly is to say "have it unlock".
That we have to work is a given.
Again, Frazetta went to art school because the teachers say he was very good and on art school, he was great from the beginning. That Frazetta worked a lot.... not even close to others contemporary illustrators but he worked a lot, yes, without effort until the malfunction of his thyroid gland which left Frazetta without the capacity of visualizing images for 8 years until they found the correct dosage and cure for his problem. If you want to know about Frazetta start with the documentary "Painting With Fire". You'll see what Berni Wrightson, Simon Bisley, and others have to tell about Frazetta. We are not all equal, we are all different.
Is clear that "the Beatles" would not have been "the Beatles" without the 10.000 hours of training and concerts that they indeed had when they started to create his great work but is clear too that there's only one John Lennon. And some are Ringo Starts, they are good craftsmen because of hours of training but never are going to create "imagine" or any other masterpiece.
I don't have kids (Possibly because I spent ten years working as a Tattoo Artist drawing every day. Tattoo artists we earn a workaholic reputation. and that cost me a relationship) and my draw sessions are and always were from 5 hours to 13 or 14 hours. That is normal for me. I sleep 4 or 5 hours normally and I'm active and awake the rest of the time.
But again, this is not about me. I realize things through my experience and put myself like an example to make a point that I think is important. Is about the CBA and if that methods to feed the CBA allow us to create better art or simply different art. I think is the second.