I maintain a balance of fiat in the centralized exchange as a parking area or reserve to conduct a trade, so I'm not sure what benefit a stable coin could provide over using fiat. Conducting a trade using stable coin pairs is not free--the exchange will still charge fees to conduct a trade in a stable coin, just as it does to conduct the trade in fiat. So I don't see the benefit or purpose of using stable coins, at least for trading.
Furthermore, the vast majority of stable coins seem to be ETH-20 based, so if you want to withdraw from the exchange or move to a different exchange, wow that is going to be expensive!
actually, you are not alone about your worry of holding stablecoin for long period of time. i guess some of the users here also have that kind of instinct that most of these stablecoins are not saying the absolute truth regarding their usd assets backing their stablecoin. as we remember, in 2019, usdt admitted they were not fully backed by usd assets, so right now, do you think they are indeed 100% backed by assets? so one mistake, and we will see these stablecoins going down. but for day to day trading, it may help the trader and usin the usdt (trc20) has still the cheapest fee among them. so you can use the trc20 network instead of erc20, that is, if it is available in the exchange.