If 1% of kids are successful, even with a poor parenting strategy, then one out of every million 3-kid families will have successful adults.
The approach described appears to be a "Authoritative" approach, using the definition at https://en.wikipedia.org/wiki/Parenting_styles
"Authoritative" is different than "Authoritarian".
Thing is, we also see authoritariana families (https://en.wikipedia.org/wiki/Tiger_parenting lists "tiger mom", "American stage mother", "Japanese kyōiku mama", "Jewish mother (stereotype)" as examples) which also have 3/3 successful adults.
How then do you decide which approach to take, if you only look at the successful cases?