I sail a mono hull (but have a lot of experience on Prindle 16 beach cat). With a mono with too much sail you heel and maybe get knocked down. In a beach cat you capsize or pitch pole. But what happens with a big cruising cat? Here in HI there have been several tourist fatalities on comercial day sail cats when the standing rigging failed and the mast killed a passanger. The Coast Guard actually made more inspections required.
How do you know on a cruising cat you have too much sail up? There is really no feed back (like you get on a mono hull) that the wind is loading up your rig.
I am not a cat sailor but I know enough to know that a well design cruising cat can be a very seaworthy boat. Look at the huge number that have circumnavigated without any problem and you will see that is a very populat boat among long rage sailors and for a good reason.
Cats are very different from monohulls, its wider beam and almost no submersed keel gives them a much bigger static stability and a much better dynamic stability. A big cat is almost impossible to capsize by waves alone.
However as you say a cat can be capsized by wind (if it has the sails up) while a offshore monohull can't.
Because of those two characteristics you don't sail a cat in bad weather or high winds the same way you do in a monohull. Cruising cats have already a small rig (compared with its RM) but in bad weather you have to take in consideration that the boat will not come back from a capsize and that means that they should be sailed with more care and in a very conservative way.
Regarding not being able to notice that the boat is near the limit I am sure you can feel that. Look at the beginning of that movie and even without being there you will notice that the boat movements indicates that the boat is near the limit (that's why I have said that the guy or was a very experienced sailor in cats or was a bit crazy).
I have been following capsizing accidents with cats and they happen almost all if not all in a single condition: Incredible strong gusting wind with sailors that are too optimistic about the conditions. Saying that it is obvious that a cat demands a more experienced sailor than a monohull in what regards sailing in bad weather, but with a floating anchor and no sails, a cruising cat has much less changes to be capsized than a similar weight monohull.
I hope it helps