Imagine a wallet (hot or not) becomes the market leader and more than half the existing bitcoins are stored there.
Then imagine it's security is breached.
If this happens at a time when bitcoin has been mass accepted and it is a dominant currency to store wealth in world-wide - then a criminal could be in possession of half the wealth in the world.....
Sounds surreal and could not happen in a FIAT system.
If you're not the sole controller of your private keys, you don't have any Bitcoins.
Most experienced people here prefer to have Bitcoins, not IOUs.
The whole point of Bitcoin is you can be your own bank.
So, I don't think this is a "huge problem".