I don't see the analogy here at all. You might as well call it a three legged stool as use the world war II analogy since the high level guys don't have noticably more in common with air power than they do with infantry nor do the mid-level guys (high and mid level, of course, subject to various definitions) have noticably more in common with armor than with air power. What they do have in common with the stool is that all three legs are necessary. (Though I'd argue that the high level guys are only necessary if your enemy actually has high level guys too--once they're dead (or if they never existed to begin with) low and mid-level guys are all you need).
Sure, high and mid level characters can often fly, but flying doesn't really give them the same kind of advantage it gives an air force. They're not untouchable. They aren't able to carry any more firepower because they're flying nor are other flying forces necessary in order to engage them.
The way I see it, the roles go more like this:
Really high level characters (16+) tend to be devastating forces of destruction like Achilles or Sampson. They can take on whole armies by themselves--sometimes. (500 first level archers with rapid shot will still take them down pretty quickly since they'll get about 48 normal hits and two crits on average even hitting only on twenties--and no character can ignore 54d8 damage in one round. Stack a mid level bard and a few clerics or some specialized hero killing arrows (GMW and Flame Arrow to give one or two arrows to each archer for when they see the enemy hero) and that damage skyrockets).
However, like Sampson, they can only be in one place at a time so it doesn't matter if they can devastate everything that's thrown at them; a force of a thousand low-level soldiers spread out across the countryside can still destroy everything or exact tribute. Even if Israel has an epic level fighter, by himself, he won't defeat the Philistines (though they'll certainly celebrate when he's dead or defeated).
Similarly, like Achilles, their presence will be sorely missed so it pays for leaders to ensure that they don't retreat to their tent and sulk for the rest of the war because you took the princess they claimed as treasure.
Mid level characters are interesting. They'll be famous for exploits on the battlefield. One tenth level wizard or druid will decimate a horde of low level orcs. However, they're not invulnerable. Massed attacks by lower level foes will take them out quite quickly and, like high level characters, they can't be everywhere at once. They are valuable, however, for their ability to withstand some of the abilities of the high level characters and their ability to potentially defeat the high level guys if they outnumber them or get lucky. One of them going missing won't make a difference to the war like Achilles sulking in his tent. Nor will a single mid level character terrorize an enemy kingdom like Sampson. However, you want to have them if you're going to win. They make an excellent center for your army and if you pull a Trojan horse type manuever, it's the mid-level guys you'll be using (you don't have enough high level guys to do that kind of thing).
Low level soldiers are still quite useful. They're the ones who need to be around to exact tribute from the peasantry or to burn your enemy's fields. If you've just got a few high level guys, several fields will be REALLY burned and a number of peasants will be REALLY terrified, but they don't have the presence to control an area and the enemy's high level guys can track them down and fight them. Not so with low-level soldiers. They can be all over the countryside.
On the battlefield, low level soldiers in really large numbers (especially archers) can be a threat even to high level characters though they burn like grass in a firestorm so they're not a really good bet to be using. (On the other hand, arrows have a much longer range than firestorms). They're a pretty significant threat to mid level foes too, but the big advantage is that they can be everywhere and keep the other guys' low level forces from burning your fields, etc. You can build some wooden stockades and station groups of low-level guys to guard the frontier for years. You can't do that with high or mid-level soldiers. (You could get them to wipe out the orc tribe that threatens you this year, but next year, another tribe will have moved in and the orcs who run away and survive may continue to raid the villages).
The other big advantage: low level soldiers are cheap. High level adventurers want thousands of gold pieces to help out for a single battle or campaign. Low level soldiers can be hired for single digit prices. If you need to keep the tribe of raiding orcs off of your frontier, a 500 man company of low-level light infantry is a lot cheaper than hiring a party of 10th level adventurers for 1000gp each. And they'll still be there when the next orc tribe moves in. (And in the mean time, they can make sure that the peasants actually pay their taxes--the high level guys won't stick around long enough for that).
So, if there's any analogy to WWII here, it's the low-level types who are strategic air power. They're the ones who will destroy your enemies' diversified resource production and infrastructure and they're the ones who will defend your frontier from similar raids. However, I think that heroic age Greek literature provides a more productive model. Achilles beats everyone but there's lots of everyone so the war goes on. Achilles goes back to his tent and the Trojans start winning the war of attrition because Hector's no slouch in the beating everyone department either. Odysseus and Ajax and Diomedes, et al can't stop him. Patroclus tries to stop him and gets killed. Then Achilles kills Hector and the greeks go back to winning the war of attrition, but Achilles is killed by treachery and the greeks eventually have to resort to a stratagem to get their mid level guys to let all the low level ones in through the gate.
If parts of the equation are lacking, you end up with the story of Sampson from the book of judges. He burns some fields really good and then goes back to his whores. (Hey, he really is a high level D&D character). He rips the gates off the city and goes back to his whores. He kills an army sent to get him with no weapon but the jawbone of a donkey that he happened to find nearby. However, he can't be everywhere at once so, while the Philistines are really scared of him personally and keep trying trickery to capture or kill him (Delilah as a mid-level bard with a really good bluff and some eric's grandma disapproved perform skills), they can keep on oppressing the Israelites like before. Sampson can't be everywhere at once and doesn't really want to be everywhere at once either. Eventually, the trick works and he's captured, blinded, and used for sport (finally, he destroys a temple and kills a bunch of them and is killed in the process--apparently the DM listened to his players' whining and let him go out with a bang). No support=an ineffective high level character.
If you want low and mid levels without the high level characters, look at the Greeks without Achilles, the Trojans without Hector, or the Phillistines without anyone who can match Sampson.
Ridley's Cohort said:
Not quite. What you have to do is reinvent the concept of Combined Arms but include D&Disms.
Moving an army without quick response teams of middling level characters who can ask for back up by higher level quick response teams is like trying to win WWII without any artillery or an air force.
Basically your normal army is your Infantry. You middle level guys are your Armor and Artillery. And high level guys are large Air Force formations. There are fortifications, too, but they are no more important than the ones in WWII unless it is the residence of a high level dude.
Your army stands on those three legs (Infantry, Armor, Air). Eliminate one and the others are vulnerable.
I can see where this discussion is going and I really don't feel like dancing around in circles over this one issue. I think I've said all that I really wanted to on the topic and if anyone else wants to weigh on it they're free to take over...
