The Safest Exchange.

So i know the whole point is its your money/coin and cold wallets are the play so you have your keys and are truely the only person who can move it/sell it. (considering your seed isnt compromised) My questions are does coinbase hold all the ETF money/coins? is it really possible for coinbase (in this point in time) to just walk away with all that money? will there ever be a day coinbase/kraken/binance are just as safe as cold storage? Whats your opinion?