I think the GP's isn't to discredit the Montessori method via counter-example, but rather to show that people have been successful long before the Montessori me

I think the GP's isn't to discredit the Montessori method via counter-example, but rather to show that people have been successful long before the Montessori method came about (as you mentioned) and will continue to be successful and productive long after the craze has died down. At the same time, just because someone went to a Montessori school doesn't automatically mean they will be a successful person. My wife worked in a Montessori school a while ago and I can't say that I agree with their method of teaching - and this is coming from a guy who went to LAUSD from grade 6 and up.