afaik, it is commonly used to refer to situations where someone makes a joke at the expense of someone less powerful than they are.

do you disagree with my understanding of the definition, or are you implying that jeff bezos is more powerful than a US senator who made a decent run for the presidency and is acting in his official capacity as such?

The latter. Certainly, Sanders isn't powerless, he's the most popular politician in the US. However, he's only one of one hundred senators, almost all of whom are beholden to or influenced by—to varying degrees and on varying issues—the members of "the billionaire class", as he would put it. Bezos's net worth is currently over $160 billion. Q.E.D.

In a world where wealth distribution was flatter, and the richest person alive had access to like $100 million (a lot of money!), that would be one thing. The distribution is not so flat in our world, to put it mildly. Not to be pat, but money is power, and I think it's important to grasp the orders of magnitude at play here.

A senator who ran and lost a presidential election is not as powerful as the richest man on Earth, no.