That's not really what most of us want out of our riding horses these days. And we also expect them to hold up mentally and physically a lot longer than those horses.
I don't really think it is a matter of "us modern folk" being "tough" enough or not. I mean, I'm pretty sure a lot of us *could* get on an unbroke horse in a day and make a go of it, probably with relative success. That doesn't make it a good idea.