I have no dog in this hunt either, and this was already mentioned above, but it's worth repeating: It is a fact that it is technically illegal to exceed ANY of the manufacturer's weight ratings.
I realize that no matter if one is at fault in a vehicle accident or not, chances are you'll get sued by someone for something. That said, if any party (be it law enforcement/insurance companies/or especially the attorneys of any of the parties involved) can prove that your vehicle exceeded manufacturer's ratings in any category, you have definitely opened yourself up for greater liability. Yes, the vehicles likely do have some percentage of margin built in to the ratings shown on the vehicle's placard. But the equipment end of it is only a single factor in one's decision, and all too often people forget about unintended consequences, and the liability incurred if/when something unplanned does happen.
If someone didn't have the full story, didn't do their research, or just believed the sales person without questioning/researching and ended up buying a tow vehicle that is not up to the task, then that's on them (or possibly partly on the sales person or dealership itself, if they made incorrect or misleading statements). But as the song goes "you can't always get what you want", and if a person wants to tow & haul more than their vehicle is rated for, my two-cents worth of advice is to trade it in for a more appropriate, right-sized vehicle for the load one wants to haul/tow. The math is easy, one just has to do their due-diligence.