The part where you said that companies do business with their customers money, I don't see anything wrong with that, that's a normal thing and they have been doing it for long and even banks does the same. Don't expect them to just cross hands and be looking after your money for you and only collecting fees, nah, they will also have to do business with it and that's one of the ways companies makes money too. And there good exchanges andb not as you have said, the good ones are there and even Binance is a good exchange and that includes Coinbase, Bitfinex and the rest of them as well. Binance got hacked but was able to sort out the problems with their customers, that's how you know a good exchange, they always sort out the problems.
I also do not see anything wrong in companies, most especially banks doing business with their customer’s money provided they are sure if the business that they get involved with, which is usually not even my problem, provided I have access to my money at any time, but the issue I have with these companies is that they don’t appreciate the people that left money with them, which they ought to have been sharing the profit with them no matter how little.
This is why I will already respect Binance exchange for ever, this is the method they use that is guarding against people dumping their coin, as they do business, they share the profit with their customers.