I think we need to have as much tools as possible to achieve better privacy with bitcoin transactions.
Completely agreed.
Whoever keeps millions on a centralized exchange is an idiot, period.
All big traders are holding coins on centralized exchanges, and if you didn't notice Coinbase exchange is custodian for most Bitcoin ETF's so far 
https://blockworks.co/bitcoin-etf
Coinbase is probably acting already like a bank. And businesses keep billions at banks. I hope that Coinbase are not idiots and have those coins in cold storage and also insured.
Of course, examplens is also 99% correct. Most exchanges cannot be trusted (I would not trust Coinbase either, but that's me). For us, here on Bitcointalk, self custody is the best option. For the big companies there's no difference they keep their wealth in a bank or at Coinbase.