I think inheritance and unchecked wealth accumulation work against meritocracy actually.
There are things that make people more efficient as a homo sapiens and we want them to enjoy those things and not to worry and stress various annoyances so they can concentrate on what they are best at.
But as you say it's obviously not like that for CEOs of big companies. Just because Bill Gates was good at selling software doesn't mean he should hold this immense power in the world and decide how to allocate resources between vaccines and cancer research etc. It has nothing to do with his meritocratic expertise (of course he pays his own experts, but he does maintain the high level control). Some would argue that this value was all created as additional value by him via the efficiencies enabled by the software and that it wasn't merely captured out of existing value. It's obviously a combination, but based on ideology people estimate it differently. We know that rent seeking and dark pattern business practices exist, as do lobbying and other forms of corruption.
The billionaire examples aren't examples of meritocracy but of rewarding luck. Nobody would say that as a human Elon Musk is literally that much more competent than, say, the best senior engineer at Tesla.
But also, beyond a certain point rich people aren't people any more, more like institutions. They just channel that wealth in different directions, they cannot "enjoy" a significant potion of it as a human being. All that money gets rotated back into salaries of others, else it would remain just numbers in databases. It cannot meaningfully accumulate. Just like if you burn a bag of cash, you induce minuscule inflation effects and everybody else's money increases in value a little bit. If a billionaire sits on his cash, it's as if he didn't have it. But when he uses it, he pays salaries and makes people do stuff. The problem is when this stuff is "the wrong thing".
I think the main argument against billionaire power is that the distributed wisdom of crowds and markets are better at allocation and deciding what's worth doing than centralizing it without limit. It's good to centralize it as long as it's about merit and related to expertise or capacity, but not beyond that. Billionaires are way beyond human scale regarding that.