The list of 6 mistakes suggests there are reasons why people might incorrectly lean towards earning to give. However I do not think that the conclusion that "probably fewer people should be aiming to earn to give" follows directly from this.
I suspect the factors that effect whether earning to give should be more or less prevalent depends a lot whether we think wealth, and the kinds of influence it can buy, will be useful tools to wield in the mid to long run (as today's young professionals reach the peaks of their careers) as well as empirical questions on what proportion of EAs are actually earning to give etc.
(On the other-hand these issues maybe so hard to predict that you think just looking at where we will be bias as a community and then trying to lean the other way is a better metric to use)
"Six Mistakes You've Probably Been Making About Effective Altruism (The Last One Will Shock You)"