In my campaign low level adventurers don't randomly face minion Demons. A Demon would never be a minion for a low level adventurer.
It would only show up as a mionion when the adventurers have reached the point where their force of being in the world is that great.
I see this differently. I would just say that such a Minion is always a Minion... the Netherworld can have faceless mooks just like any place else.
Now, they're highly
professional faceless mooks, just like a unit of SS panzergrenadiers would be. Indvidually those troopers are not a bunch of little Audie Murphys or anything... but they do hit what they shoot at and they are totally vicious against enemy mooks.
To carry on with your GI Joe / COBRA analogy, high level Minions are like elite commando or ninja types. They're still not "named characters", and they still go down with a single lethal shot, but they are unquestionably good at what they do (which is why they haven't been shot through the heart until now... now they're facing Snake Eyes or Achilles or Chuck Norris or whomever and are about to learn about the "next level" that it's possible to take martial prowess to).
On the old complaint of "it feels like a videogame/WOW": the 4E game I'm playing in kind of does. But I think it does mainly because the goons have arbitrarily high AC and HP (even half-naked bare-knuckle brawlers are showing up with like a 20 or 21 AC [barely attainable by our own party], dishing out damage with their fists that is the equivalent of a sword attack, and having a million HPs). It's the whole thing about "Well, the pirates in this area are only level 2 because this is a newbie area, but the pirates in this other area are all level 40 because that's an area for experienced characters."
So you do wonder, as you're trying to think of the fantasy world, why Thundersnout Orcs all die in one hit to low-level schlubs, but the entire tribe of Snowfur Orcs are epic level just because they live in a different neighborhood. Or, more to the point, why all the bar bouncers you faced at 1st level were 1st level bouncers, and now at 11th level all the bar bouncers are 11th level bouncers with the Dalton Paragon Path.
It's like being on a weirdass treadmill. Your character never even seems powerful because everything levels up in lock step with you.