Might there not just be a semantic issue here? Unless I'm mistaken you seem to be equating ambition with doing very well at something, such as successfully climbing a corporate ladder. And that's an absolutely reasonable ambition that's also more attainable than ever, as you mentioned. But I think Paul Graham was speaking of ambition in terms of revolutionary or world-changing type stuff.
For instance in a parallel world Elon Musk ends up going to work at Boeing and perhaps even gradually works his way up to becoming their chief engineer. But in this world it's unlikely he would have even been able to create fully reusable rockets. That was not only an expensive and extremely high risk venture, but one which many key people, such as Tory Bruno (CEO of ULA - a Boeing/Lockeed partnership), were aggressively dismissive and even mocking of, until SpaceX proved it. Let alone all his other ventures like Tesla or big picture goals like creating human colonies on Mars.
For instance in a parallel world Elon Musk ends up going to work at Boeing and perhaps even gradually works his way up to becoming their chief engineer. But in this world it's unlikely he would have even been able to create fully reusable rockets. That was not only an expensive and extremely high risk venture, but one which many key people, such as Tory Bruno (CEO of ULA - a Boeing/Lockeed partnership), were aggressively dismissive and even mocking of, until SpaceX proved it. Let alone all his other ventures like Tesla or big picture goals like creating human colonies on Mars.