You know, I wish they had taken a page from 3e and had a class/level demographic. I don't even care what the numbers are, just that it provides a baseline for people to use for "low/normal/high" magic.
E.g. in a city of 10,000 it would be typical to have wizards of 9th, 8th, 7th x2, 6th x2, 5th x4, 4th x4, 3rd x8, 2nd x8, 1st x16 and clerics of 10th, 9th, 8th x2, 7th x2, 6th x4, 5th x4, 4th x8, 3rd x8, 2nd x16, 1st x16. This sets a baseline assumption that 52 casters could create Continual Flames.
I personally like settings having high level casters while also thinking this is kind of crazy pants for a city of 10,000, but it gives a common baseline for discussion (and also explains why 3e was, relatively speaking, knee deep in magic).
While I'd like that, I don't think they should put that in the rules part. This kind of statistics define worldbuilding. In this thread we have very different opinions on what the world should be, from "magic is so rare that only a handful of wizards in a country can brew a cure light wounds potion" to "every village has a wizard, a druid, and a cleric". And that's for the "wideness" of magic. Some will prefer worlds where higher magic is a thing of legend, other will want several casters of 9th level spells in a university, not something common but common enough for a kingdom to have several of them.
I think explaining to new DMs how to build worlds where the players won't be all the time "wtf?" if they approach it logically and ask why the court druid of a besieged fort didn't just spend all his spell slots on goodberries instead of having half the garrison starving when it was the premise of your first homemade adventure.
Also, explaining exactly how PCs are different affects play. Because, OK, I have zero problem considering the rules are for PCs because they're exceptional. The PC fighter can cleave people in half and take punishment that would take down thousands of men, sure, he's having fighter levels and the rest of the people are common people with a lousy stat block, and the cleric is actually blessed by his god to receive spells while everyone else is just either a priest with no magical power or a smidgen of power from an acolyte level. I am very OK with that. But if "players are specials" that means that when a wizards cast a measly 3rd level Fly spell, it's a feat unheard of outside of legends. It will awe people from these settings as much as it would awe us if we saw someone doing it in real life. It's not a simple explanation to say "the PCs are the only one that can do the things in the rules". It may have severe worldbuilding consequences, maybe up to having peasants with pitchfork going after them. People suspected to have the power to fly have historically fared badly in some places -- though it wouldn't fit in current settings.