Totally agree with you on that. But the question posed is the aspect of the situation that is usually ignored by the "thin folder only" guys. That even if a tough knife can't cut as well, they still cut well enough for maybe 90 percent of all cutting
tasks.
What I'm asking here is, What cutting tasks that thin folders can handle, that tough, thicker bladed folders can't do well enough?
My non-knife coworker was arguing with me 2 days ago, why do I need a knives on me at all. I said: to cut packaging, open letters, occasional small wire, food, etc, that besides the fact that I like knives.
His counter argument was similar to yours

Most of the things he can tear, break, pry open with screwdriver or pen, or use scissors, teeth, etc... That's "good enough" for him.
My point of view is, if I am to use a tool, ideally I want the tool that does the job the best/easiest/fast/precisely. And thick folders by definition can't cut as well as thin ones.
As far as hard use goes, those thick folders hardly make good choice for batonning, short blade after all. Prying is another heavy duty task often cited and I've seen quite a few broken tips on BF too. Besides, chances are the handle will fail, or pivot. It is not a job for a folder...
For sure there are tasks that require a knife optimized for cutting but what about the vast majority of cutting tasks?
So, if a folding knife isn't optimized for cutting, what else it should be optimized for?