To be fair they are scaled by area, but I think I agree with your main point. If you come back to a group of early goblins late in the game they will still be level 1-2, but there are essentially level 3 areas, level 4 areas, level 5 areas, etc. As you say this is how they did it in DOS2 and many CRPGs and I think it works to an extent.
I definitely agree that having "commoners" at high levels is nonsense. I would also like to see a little less upscaling of monsters. For example, a goblin in 5e is CR 1/4. If you face a group of 4 goblins as a level 1 party they can give you some trouble. If you face a group of 4 goblins as a level 5 party you will stomp them easily. If I want my level 5 party to fight goblins as a DM I might hit them with a dozen of them and a handful of ogres or some other allied creatures. I realize this isn't always ideal in a video game format but it gives a much better sense of progression when you are strong enough to mow through multiple goblins in a turn. Giving the monsters levels can be interesting but takes that sense of progression away.
