Effective Altruism asks "what's the most I can do?" and come up with the answer, "become a king and give my(!) money I earn(!) to effective charities".

That only makes sense if your starting place in the system makes becoming a king possible.

Meanwhile, if they asked "what's the most we can do?" then the answer is unlikely to involve kings and more likely involves changing the system that gives them the opportunity to be kings.