I think this is true. There was an article on HN the other day about how Moderna has already re-organized its leadership structure around AI.
It makes sense to me that AI could conceivably already be as good at making the hard, data-based decisions that CEOs make, and that, therefore, they could one day be replaced by AI. Meanwhile, you've got the soft skills part of being an executive, which humans are better at (as long as the people they deal with are also humans). So, you could split that CEO role into two parts, each specializing in half of what a CEO today does. Both roles would probably do a better job than the median CEO today, and get paid less overall.
But that "not anytime soon" part is the only thing I disagree with. Because I just don't know how long the timeline is for stuff like that. It can change pretty fast.
Will they really get paid less? The feeling I have now is that people are paid a lot not because of what they do, but because of the potential damage they can do in case they fucked up. E.g. CEOs, lawyers, etc. Moving some of the work to AI doesn't reduce the risk, so they should have the same pay in my mental model.
Plus C-level executives typically don't lower their pay, and IMO investors apparently don't care that much about their pay, I can't see a reason why their pay will be reduced (significantly).