Follow-up: I honestly could give a fig what any WotC publication has to say about world building, so I freely ignore anything that doesn't work with what I want my world to be like. Objective realism is also not a concern because if even 1% of what is in the PHB, DMG and MM existed the world would be so utterly transformed as to be unrecognizable, not merely the Middle Ages/Renaissance, but with magic and monsters on top (like so many fantasy settings). Consider the thread over in the D&D sub-forum on how transformative a single decanter of endless water would be for a civilization.
So this is just not a problem. My going assumption is that the PCs are only remarkable in the sense that Indiana Jones is remarkable - the story revolves around them, and they are unusually intrepid and skilled, but not superheroes. My current home campaign is level 7, so in the last game when they ran into a group of pirates that they wound up fighting, those pirates were tough enough to provide a suitable challenge for level 7s. Because that's what makes sense in the story, and makes it fun. There are times when just rolling over some hapless mooks could also be fun, but not often. For us. YVMV.
My issue with this is that it changes what
level 7 means to the PCs.
Is level 7 "you are a competent warrior", or is it "you are the best swordsman in the empire"?
So when you face pirates, are they competent warriors or are they strangely better than the best swordsmen in the empire?
This has knock on effects beyond world building -- in-adventure impacts. If PCs fighters at level 7 are world-class fighters, then seeing a dozen dirty pirates the PCs can very safely assume they aren't all world-class fighters. Because that would be ridiculous, wouldn't it?
In turn, this kind of information about the world means that the PCs can look at enemies, and have an idea if this is a "run away don't fight" or "curbstomp" situation, without the DM having to always telegraph it manually.
It also means that the DM is "forced" to up the stakes for higher level PCs. If level 7 PCs are "best in the empire", a fight against 15 pirates is not a suitable conflict, unless said pirates are somehow supernaturally insanely powerful. And if they are, the stakes are probably more than "we found some pirates".
A problem with D&D that many DMs complain about is how it their adventures stops working when players start getting L 5+ spells. But if the stakes of the game are consistent with the players level, when planeshift shows up it is appropriate for the game. L 7 they are world-class combatants; L 13, they can take a sunday brunch in heaven, L 17 they can reshape the world with an action.
OTOH, if at level 7 they are fighting mook pirates who are 75% as good as them, and at level 11 they are fighting mook pirates who are 75% as good as them, and and level 15 they are fighting mook pirates who are 75% as good as them... because you scale foes up to match the PCs capabilities, without scaling the
narrative scale of the PCs abilities ... then suddenly entire categories of world-shaping spells start breaking the game.
I mean it can and does work! It just is an issue.