I try to stay as short as possible, to present my point of view.
1. I don't want to say that either melee or ranged is easier or more difficult
2. Melee players can support each other with linear growth, which means that every additional melee fighter is worth an additional melee fighter. Perhaps it's even at a degrading rate, since there can only be so much melee players around an enemy without teamhitting everyone and his mother. Archers can support each other exponentially, which means every archers helps the team even more than the guy before him. It's the famous point when you have enough Space Marines to stop an infinite amount of Zerglings, since they can't get into reach. But there can never be a certain amount of Zerglings stopping an infinite amount of Space Marines.
3. This effect starts a vicious circle, since if there are enough archers, they seem OP. If they seem OP, the average cRPG player skills into that class/build, which means there are even ore of them, making everyone of them more OP. It's a self-fullfilling prophecy.
4. Since the effectivity of an archer is determined by the amount of his fellow archers on the server, it is difficult or even impossible to regulate their abundance by tweaking their stats like damage or missile speed. If there are less archers than the calculated average, they are UP, if there are more they remain OP. It would a bad and unfair solution. If anything, a single archer is heavily UP, if you try to be fair and look at his stats compared to an infantry or cavalry player.
5. Playing infantry requires a high amount of teamplay. In difference to the other classes the infantryman require the support of his fellow team members. If infantry players are cooperating with other players, and this group of cooperating players reaches a certain size, it becomes almost unstoppable. On the other hand, if everybody runs around like the average autowalker-Rambo-lemming, no wonder infantry dies like flies and looks almost unplayable and subpar compared to cavalry or archers. If the different classes of infantry players cooperate, they negate their weaknesses and counter all the other classes. On the other hand a single infantryman who has no overview of the general course of the battle is easy prey and already dead. This is the other side of the archer problem: the alternative is unattractive to most players.
The only way to finally get a grip on the ranged problem is to control the amount of ranged on the servers. As I stated above, nerfing or buffing certain classes won't help and is a bad and unfair solution. Instead the incentives to play a certain class on the server should be changed. I made a suggestion some time ago that a certain percentage of your XP is determined by the class you play. The less people on the server play your class, the more XP you get, and the other way round. I wouldn't do this with money, since it should not be made IMPOSSIBLE to play certain classes, just not really rewarding. Another thing which bothers me since I play cRPG is this horrible philosophy to want players to stick to their build. Yes, roleplay wise that's nice, but it's horrible for all the other aspects. If people could respec always or at least more often without those negative drawbacks, and if the marketplace would disappear (it's the worst idea ever and I am honestly shocked someone who can make a game like cRPG can can make such a decision which is as stupid as it gets before crossing the mentally disabled line.) and everyone could reset his loompoints when he wants to, players would be more flexible, the devs would notice unbalances much faster (since the players always notice them first and then you can recognize OP builds by their abundance), and most important of all: it wouldn't be so much of a kick into the face when your precious build gets nerfed or even unplayable at all, which is not your fault and yet you get "punished" that way without any compensation. Yeah, yeah, marketplace, I told you what marketplace is worth a few lines above.