People have sailed/drifted across oceans in the most unlikely of craft and made it.. others have departed on well prepared, so-called 'proper' boats and not. But the opposite happens too. Having a good solid well built boat means that barring catastrophe the boat itself should not become an issue. The people on that same boat may well do so.
I'd say on average most boats will survive more than most people would want to put up with.. but that doesn't make them ideal for the task.
Like so much else boating it's all about the compromises chosen and the resultant 'sum of all the parts' of the equation. You see people being taken off floating, substantial vessels that should not have been abandoned, you see people making poor decisions about entering passes or harbours and ending up aground, seriously damaged and occasionally with fatal results.
I think there are certain boats that I would not take outside a harbour, but every one of those is probably owned by someone that thinks it would be fine... at least until they try it..
There are plenty of books and stories out there of remarkable sailors, managing to survive ridiculous conditions on boats some would say should have sunk... others survived long periods in a raft after a catastrophic collision. And there are soo many more uneventful, non dramatic successful cruises carried out by all sorts of people all over the world.
The boat is just a part of it...