Manbearcat
Legend
Let's take that falling example. If I decide that I want to add more realism to falling, I can require a death save from any fall of 20 feet or higher, with a -1 penalty for each additional 10 feet. That would give your 30 story fall(300 feet) a -28 penalty to the death save. Good luck surviving that fall over and over again. It still won't mirror reality, but it is in fact more realistic.
D&D is not now, nor has it every been "entirely fantastic." It has many fantastic elements to it, but there has always been a good measure of realism to it.
The problem with adjustments like the above, Max, is that the rider effects to stuff like this quickly either becomes clearly arbitrary or “not D&D.”
The kinetic energy of a body at terminal velocity has less kinetic energy than that of an Ancient Dragon swinging its tail (even if for some strange reason you assume 2/3 the acceleration of a human punch). I think people can intuit that without performing any math.
So if the mechanics dictate your heroes die at an extremely high rate due to high falls, they better not be wading into melee with Ancient Dragons. So that ceases to become one of the foundational tropes of D&D.