It's not too bad like what you say. A stable coin will give a profit where the price of other coins drop.
Stable coins do not provide profit if the price of other coins is increasing.
For example:
1 ETH = 230 USDT
If the ETH price drops -10%
230 x 10/100 = 23
Then the stable coin holder has made a $ 23 profit.
And if they repurchase ETH,
$ 230 + $ 23 = $ 253
1 ETH + 0.1 ETH = 1.1 ETH
Well, this will be the opposite if the price of Ethereum rises.