As soon as you create institutionalized positions of authority you ensure that they will eventually no longer go to the “the wisest, most knowledgeable, or most capable” but instead to power-seekers

This is a great anarchist critique of MLism (and basically any institution). I would even add to it -- if you are able to create a legitimate, actual meritocracy, you're likely to get at least a well-intentioned actor who will bend that system back towards something more corruptible if only to keep doing things that may be genuinely good. Over time and personnel changes this could open the door for power-seeking bad actors.

If we're talking about fundamentally reshaping society, though, I think long-term we could get to a point where a "real" meritocracy could work. You could make leadership positions truly thankless jobs, even at the highest levels (strip away most of the perks, prestige, and little displays of power). You could have qualified people drafted for those jobs for fixed, non-renewable terms. You could have recall votes a possibility for every position, you could have "real" journalism (i.e., not for profit, with access not determined by those in power), you could have a deep cultural taboo against ambition for ambition's sake, you would of course have a much improved education system that among other things swaps capitalist indoctrination for leftist political education.

"We could run an actually good organization at national or global scale" is not too big of a dream compared to anything else leftists discuss.