Keep in mind that BTC like altcoins are paired to USDT. USDT can't be trusted as they are not backed by adequate collateral.
There is always another pair option like BTC - USDC, or BTC - BUSD which has a regular audit and proven that they are backed by adequate collateral

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Actually, Celsius, Terra, FTX crashes all prove that if you don't do self-custody, you're going to pay it sooner or later. There are two kinds of centralized exchanges; those that have been shut down, and those that will.
Well, there is no permanent in this world, even the strongest kingdom crumbles and Dynasties end, so it isn't surprising that these centralized exchanges shut down one day. Even Bitcoin can possibly be dethroned by another cryptocurrency one day.
You wanna buy the shittiest coin, hold it, and hope to become rich one day? Go do it, but for the sake of you, hold your keys. If there aren't any clear, available methods to do it, start questioning the specific altcoin's growth.
I greatly agree, better to have our wallet holding our worthless tokens than entrusting it to someone else.