Time and again it's laziness and incompetence rather than hacking sophistication.
Until DNS and hosting is totally resistant to hacking I'm not going to be 100% convinced a dex is safe.
Right on. This has been true in almost all the cases of hacks of exchanges, going all the way back to Mt Gox. Negligence, nothing more. Lack of training for employees, lack of the most basic security and accountability measures. Just plain absurd arrogance to think that you could handle that much amount of funds and leave them out in the open, basically an open invitation and a hack waiting to happen.
All these guys have been guilty of negligence and this should be pointed out.
I'm not convinced DEX is ever going to be 100% safe, I think there is no such thing. But for current popular deployments, except for funds locked in off-chain escrow, at least if a host or server of a DEX is down, all you lose is access, with funds still firmly in your control.