I have no data on this, but my spidey-sense says you're both wrong. If I had to put money on it, I'd say:
- success is correlated with hours worked (though it's by far not the only variable)
- education is more strongly correlated with success than birth is
- education is strongly correlated with birth
What do you reckon?
It has never been true. Success has always been primarily correlated with the circumstances of your birth. This is not an antiquated notion so much as a fabrication invented to trick the less fortunate into putting up with it.
In that sense, it is as relevant today as it has ever been.