I have a hard time believing in a country filled with lawyers that a car specifically designed to hold five adults it is actually unsafe to do so.
Prove to me that a small car is "specifically designed to hold five adults." You can use whatever
manufacturer-provided information you wish, but engineering data matters, marketing data doesn't. And I seriously doubt you'll find marketing materials showing a car overweight. They're not dumb.
"It has 5 seats, so it should hold 5 adults!" is not proof it's designed to hold 5 adults. It may very well be able to hold 5 small adults, but you can't just ignore the engineering data because you want to.
In small aircraft, there are planes with 4 seats that simply won't carry 4 adults. A Cessna 172 is mostly a "2+2" airplane - two adults up front, two kids in the back. You can sometimes fit four adults depending on size/weight/fuel, but if the question is "four adults in a 172," you'd better have your weight and balance sheets out, because you're probably going to be over gross, and you stand a good chance of having CG issues. Four adults and baggage? Just not something a 172 will do.
A 182 is a four adult airplane, but, again, check the W&B, because you're not going to take four adults, baggage, and full long range tanks without being badly overweight (unless they're particularly skinny adults).
Heck we have quite a few plus sized Americans that would technically overload* that corolla with just 2 people.....This is also in a country where Toyota settled for a billion dollars with old people despite doing nothing wrong.
I don't think you're fitting 400+ lb people in a small car.
And I'm going to assume you didn't
read the reports on Toyota's accelerator system/firmware/etc, because that was a steaming pile of crap that shouldn't have been in a roadworthy vehicle in the first place. It was vulnerable to a wide variety of failure modes that would lead to unintended acceleration. Did any of those trip? No idea. But the design of that particular module was so awful that it could easily have been responsible for it.
I've towed 4500 pounds with a 3300 lb tow vehicle. Speeds were in the 25 mph range on flat ground in very light traffic, small town. Worked perfectly.
Yeah, but you understood the limitations and conditions, so were able to reason about it. I've flat towed a pickup with an old Subaru before - thing probably outweighed me by a factor of two, but it needed moving, I was around, and there was someone in it to run the brakes.
Also, that 5th wheel abomination you linked is one of the scariest things I've seen - and I've seen some pretty beat up cars in my day. Driven most of 'em.