It seems to me that ultimately morality of someone's economical behavior is determined not by how wealthy they get, but by the relationship between them and their partners. When I buy a Tesla, I voluntarily choose to part with a large amount of money, because the value of the Tesla for me is higher than the value of keeping that money in the bank or spending it on something else - and Elon Musk delivers my Tesla as promised and gets richer, for he values the profit he gets from his stocks growing higher than he values one of his thousands of Tesla's. If Elon Musk gets rich by doing this, then he is not doing anything wrong in my book. It is another matter when Elon Musk gets into the government and uses his friendship with Trump to push through proposals that harm competitors of Tesla and advantage Tesla and Musk personally.
But a better question is this: what is the source of the latter? Is it that billionaires are somehow intrinsically corrupt and inevitably use their money to buy up political power? I do not see how this can be the case: even if all billionaires were intrinsically corrupt, in a good political system any attempt by them to bribe someone would result in their incarceration.
A more plausible explanation was provided by Friedrich Hayek in his "Road to Serfdom". The source is the fact that the government is the only organization in the country that has a legal power to coerce individuals. This is where corruption originates. There is no corruption on a free market where all transactions are voluntary and anyone can walk away from an interaction they dislike. But when the system is more akin to a "king of the hill" game where whoever gets into this exclusive club of political players gets to force others into interactions they do not want to partake in - and have the law on their side - then everyone who has enough resources will do their best to befriend the king, or, even better, take his place.
Which is why the economy should be separated from the government. It should be impossible to buy any political favors legally, and for that, in turn, it is essential that the government is extremely limited. When the government is nothing more than a guardsman against coercion and violence, then there is absolutely nothing to gain for me or anyone else from buying "political credit". Being in the government actually would be more of a burden than an advantage, and only people who genuinely wanted to do good in the society - at the expense of their time and money - would be interested in pursuing a political career or proactively interacting with the government.