This ignores legal realities about property and transferring wealth. When she buys him for 400mil, she will briefly place the money in escrow, reducing them to 700 and 400mil. Then, when he becomes her property, Taylor also gains his assets, reaching 1.5 billion when the escrow is released.
And house slaves thought they and their families would have a better life by supporting the power structure that enslaved them to begin with. That doesn't belie just how fucked up it is that some shitty Taylor Swift fan account is insinuating that a white billionaire could literally purchase a black man.
Most of that money comes from sales of her art, not from the exploitation of surplus labor, so it's marginally better from a moral standpoint. Though she would still pay more taxes if it was up to me.
A majority of her art up until recently was not created by her, but rather many professional songwriters. So even the whole, "not from the exploitation of surplus labor" doesn't hold water. She's just like the rest. Hoarding that wealth, when it could be used for the betterment of many lives, is criminal, in my opinion.