A better comparison would be a stock brokerage that took your money to buy specific stocks on your behalf but then did something totally different, including “investing” in illiquid assets.
If they had just bought the stock you requested, then they could just liquidate your stock at market price when you said you want to sell.
This was not the situation that FTX was/is in.
Instead, the way FTX allocated money/assets was suspicious (at best) if not flat out irresponsible and deceptive.
Also, FTX was not and is not a bank, and the idea that this is levering in the same way regulated banks lever is laughable.