There are still some exchanges that are reliable and save to keep your bitcoin. Although you have said it, most people save their coins in exchange due to the higher transaction charges, but what Op said is a great idea that will help many people. 
 
Take an instance where you don’t know if TON and you want to send out bitcoin, and the bitcoin you are sending in is not small, so the higher transaction free can be enough for someone who wants to start investing in bitcoin. Like me, when I start a bitcoin investment, I start up with just $30, and that is just some transaction free to send out bitcoin. If you use exchange to swap your money to USDT, that transaction free will be absent, and it will be so useful to you in the future. I think that is what the OP is trying to explain. If we look deep, everyone needs a discount, even though I know you are also trying to save people from trusting those random exchanges.