> ...it's 10,000 hours of practice the right way and ideally with an effective teacher.
There are a few problems with this.
One is that it's unfalsifiable. For any given case of failure you simply say the practice was not deliberate enough.
Two is that we do not have that ideal environment for deliberate practice. There are only so many music conservatories. That's a resource problem.
Three is that we do not know what actually constitutes proper deliberate practice, and that the informational component of the practice is a lot more important than the hard work component. In the common regurgitation of this phrase and the principle, it's typically told the other way around - as if we have already figured out how to deliberately practice, and you can just go do the work. See my rather large post above.
Finally, practice even with the best information can't compensate for motor problems and other related issues, at least, I don't see how. There are most likely genes that code for various degrees of the quality of the physical apparatus, and then there are people whose body is more messed up than normal in general.
> There are probably thousands of people who studied piano from a teacher who was a professor at a music conservatory in Russia. They can't all become world-class.
This is an important point. If you have thousands of people trying to do something, they can't all become world class. Even if you have the absolute best methods, if they are more or less equally practiced, you'll get a homogenization effect and the best practitioners would be purely random. The more this happens, the more inappropriate it is to tell someone that they can become the best, because it requires some weird negative assumptions about all the other participants. It's not even work or genetics at that point, but just general randomness. This is not a problem that necessitates solving, it's an artificial one.