It's true that 'not your key, not your coin', and that there are several wallets and services available to cover yourself.
There may be a point at which any cryptocurrency (whether Bitcoin or another) is held on exchanges/wallets run by small/new companies.
The small players have limited resources. How do they ensure they are sufficiently protected? Why don't there be hacks every other day?
Exchanges are definitely not a good place to store your funds long term.
"Not your key, not your coin" is a mantra that has been time tested and every time there has been a hack, this should have been applied beforehand.
Whilst I agree that people will inevitably have to use exchanges/hosted wallets sooner or later, they can minimize this risk by withdrawing periodically and sweeping the coins into a wallet that they actually own.