Interesting thought that sprang to my head the other day after watching Critical Role. One of the thing that keeps the show interesting is how everything they deal with is generally the same level as the party. Which makes some sense. But in another way, it does not make a lot of sense.
It comes down to a game philosophy. How powerful and heroic are your characters? How much do they stand out from the general population? Are the players Avenger level powers? Equivalent of Gods amongst men? Or are they just average for the population?
In the past in my D&D game, I took the approach that the world around the players was pretty ordinary. And that they stood out, they were the heroes of the world. As they advanced in level, they become Super Heroes. I wanted the boys to think like they are powerful and able to do extraordinary things.
From watching the show I am getting a sense of how to do things differently. As the characters progress in level, there is no real reason why those that they interact with do not increase in level and power as well. Your foes will have a lot of hit points. They will also have access to a lot of spells and powers.
I am not arguing for transforming the game to Monty Haul. And here is where the D&D 5E rules really help and come into play. The way they wrote the rules is that, while useful, magic items are not the be all end all for characters. Instead, it is the abilities of the characters that make them powerful. D&D campaigns can now very easily be leveled up like boats in a rising tide.
I look forward to taking this new approach when I take the boys into the new setting. The world will be full of creatures at the same level as they are, and will not be that noticeable.