Is buying before Ex-Date In a LOW TAX BRACKET free money?

Let's say my income is very low as a retiree, student, etc.

To a hedge fund or rich person owning a stock, if they receive a $1 dividend it's really not worth $1 because of taxes. It's probably worth $0.70, so the stock should drop by (1- average stockholder tax rate) \* dividend amount in theory, right?

People cite the post-ex date as dropping exactly by the dividend amount but given taxes I dont think that makes sense unless this theory is just empirically wrong and observations prove else wise.

So if you're in a low tax bracket is this an actual arbitrage or not? I haven't heard this before anywhere