Have had this discussion in ENworld before. I've run it RAW and have run it with no damage cap. Neither are entirely satisfactory. Falling in the real world is often more bizarre and unbelievable that in our fantasy games. As just one example, read the story of
Alan Magee. He fell 22,000 feet after jumping from his damaged B-17 bomber, only to discover his parachut had been torn and rendered useless. He crashed through the glass roof of a railroad station and survived with several broken bones, severe damage to his nose and eye, lung and kidney damage, and nearly severed right arm. This is what he looked like in 1995:
Not bad for a guy who fell 22,000 feet (
source)
Popular Mechanics covered this and four other extreme falls. As the article explains: "Anything above 10 or 12 stories and you've reached terminal velocity. So a fall from 20,000 feet sounds dramatic, but there's really no difference from a 500-foot fall." 12 stories is about 120 feet. So 12d6 falling damage. So as early as 6th level, a Barbarian with near-perfect hit dice rolls could be almost guaranteed to survive nearly any distance fall if you follow real-world physics and cap falling damage at 12d6 instead of 20d6.
I don't like the D&D rules because (1) your level and hit dice shouldn't be the only deciding factor and (2) falling damage is too low for shorter falls.
If/when I run D&D again, I'm thinking of homebrewing so that falling damage maxes at 12d6 but has a percentage chance of system shock. If you fail the percentile roll, you die instantly, but you can spend an inspiration to go to 0 and start making death saving throws instead. The question is what should be the chance of insta-death. I would like to say 95% but perhaps that is not in the spirit of 5e. Also, it might just be more elegant to say insta-death for any fall over 120 feet but you can spend inspiration to instead turn that into 0 HP with death saves.
P.S. Interesting NPR article on topic:
https://www.npr.org/sections/health-shots/2018/08/24/641395468/surviving-a-big-fall