The 10,000 hours predates Gladwell. He just wrote a book based on existing research. I haven't seen anything that actually disproves the assertion (again, it's not Gladwell's). Do you have references?
So it's not clear that 10,000 hours is a falsifiable statement.
It not as tightly defined as we'd like, but I think it's still fairly close to falsifiable. For example, I think the Dan Plan is a good experiment. He has a pro golf coach and clearly is doing deliberate practice. It's only one data point, but I think if we get several people like Dan who tend to fall on one side or the other then I think we have strengtened or weakened the theory significantly.
that people made genuinely great discoveries without needing 10,000 hours, and there are other examples where people did 10,000 hours of deliberate practice without achieving results. I actually found a critique (can't really find it now) which convinced me that he fudges data to support his claims and sell his books, author examined his references that support MG claims and found many to not be quite supportive and that it is a pattern that is present in most of his books.
His books are entertaining read, well written and all, just not reliable scientific information.
That amounts to a huge, ill defined, fudge factor that allows you to discount any counter examples.
So it's not clear that 10,000 hours is a falsifiable statement.