Montessori only works if you are a gifted or diciplined child from the start. For those that lack that in their personality its a really bad match.
On the other hand, it's really visible that the method doesn't work for everybody.
So, I think that "it's for gifted children" is the wrong conclusion here, but there is something to discover on that line.
[0] https://en.wikipedia.org/wiki/Maria_Montessori#1896%E2%80%93...
I have observed children one might believe as ‘stuck’ in an unruly category transition into one that seems ‘gifted-from-the-start’.