The variable this ignores, however, is magic. [/QUOTE}
Good point. I did somewhat account for this in that I think it is viable to consider Early Industrial as a realistic equivalent, considering the prevalence of magic in some campaign worlds. But this really depends the world itself and the assumptions built into it by the DM--as you say. Is magic closely guarded by wizardly orders who don't share it with the masses, who thus do not receive any such benefits that you mention? How rare is it? Etc.
And a balancing point: the existence of magic, and fantastical creatures, makes a typical fantasy world far more dangerous than our own world, at least in that it adds potential threats that our world doesn't really have. On the other than,
this point is further balanced by the general lack of frequent plagues that have occured in our world, or at least they usually aren't nearly as common in most fantasy histories.
You're assuming that training has to come from someone else, right? But what about self-training?
Yes, which is why I see no reason that there could be a plethora of low-level classes--at least fighters, rangers, and rogues--in most populations. this also furthers the idea of a "bottom-heavy" pyramid (or beaker).
...my world would probably be somewhere between these two on average, though the actual numbers would vary widely depending on culture. For example it's quite possible that 3 Elves out of every 4 are levelled now or have been at some point during their lives, where it's also possible that of a community of 1000 Hobbits you'd be lucky to find one with any levels at all.
Yes, I like this distinction and thought of it at the end of my long post, which is why I mentioned other factors--such as specific groups. I would imagine that drow would have a very high percentage of leveled individuals, for instance, due to the dangerous nature of their habitat.
My incomplete thoughts on this lead me to conclude that the shape of the distribution isn't a nice neat triangle with low level at the bottom and high at the top, but more like a beaker: triangular-ish at the bottom but morphing into almost a narrow tapering tube or cylinder at the top, with a very high upper extreme.
Yeah, I like this. It is also why I would think more in terms of tiers than levels. If a world has, say, 50 individuals at epic tier (16-20), they can be distributed in any number of ways, and it will always be shifting.
I'm reminded of "cat years." Most people think it is x7, but it really varies within different age ranges.
One last point. A factor that I didn't consider when writing the longer post, but thought of while reading yours, is that "abandoned campaigns" could add an element to the mix. For every campaign that makes it to 15th+ level, there are many--dozens, probably--that never make it past 5th level. This might be the "real-world" corollary to the pyramid/beaker shape. I mean, it isn't unlike the fact that all of us have countless unfinished projects for every one we finish.
I don't think this formula is any more absolute than the original one I came up with, but it does provide another angle and guideline to think this through. Let's say, for instanace, that about 10% of starting campaigns make it to 5th level, and of the PCs, half survive. That means that for every 100 1st level characters in starting campaigns, 95 of them effectively "retire" (corollating with abandoned campaigns) or die before reaching 5th level.
It doesn't have to be those percentages, but that gives us an idea. If we take the same approach for every tier with an arbitrary one millionish leveled characters, we get:
1 million at 1st tier (1st-4th)
10,000 att 2nd tier (5th-10th)
100+ at 3rd tier (11th-15th)
5 at 4th tier (16th-20th)