Hordes are a product of the mission planners.
Not really. The one thing the mission planner has the least control over is who shows up for the mission. And 30-40 plane missions are pretty rare. If you see a horde that size, what most likely happened is that 12-15 guys joined the mission and 20-30 other guys decided to follow along for easy kills once they saw a big green blob dominating an enemy base. After that, if it doesn't fizzle out, the horde pretty much takes on its own momentum without anyone leading it and usually without missions being posted. Usually half the guys, sometimes all of them, don't even care about taking bases, they just want to circle around competing for vulches.
Also, I think you vastly overestimate the extent of tactical control the mission leader is able to exert over the people flying a mission. Try running a big mission sometime, it's like herding cats. You have a pretty random group of guys who happened to show up, it's not like running a squad with a well-defined command structure and members who've trained and worked together. It's hard enough getting a mob like that to follow any but the most basic tactical plan - climb or NOE, flatten the field or leave it up - and assigning targets so at least everything vital gets taken down; anything beyond that is just about impossible to coordinate. And you have no idea of the skill level of most of the guys there, so you can't rely on anything getting done without multiply redundant assignments. Sending half the group to do something else, somewhere else almost guarantees that something vitally important won't get done right here, right now.
And you never know who's actually going to show up until it launches, or even how many - people pop in and out, and some who have joined will get bored and up somewhere else, or not have landed yet, and so miss the launch. Sometimes you have 8 or 10 people actually in the mission 30 seconds before launch only to find 20 actually taking off. Sometimes it's closer to the reverse. Telling half of a motley gang like that to land, up at another base, and go hit a different target isn't remotely practical - for one thing, they didn't sign on to join your squad or make you Generalissimo for the evening, they signed on to fly along for that one mission, the one you posted. They may or may not have any interest in doing anything else you have in mind.
And most guys who plan and run missions - and anyone who wants people to show up the next time he runs one - think it more polite to
thank people for joining than to tell them to buzz off.
In essence you are looking at hordes as well-coordinated actions of a few squads working closely together to a common purpose, when they aren't like that at all. A mob of 40 players cannot be subdivided into two or three well-coordinated, skilled groups of 12-20 players the way you suggest. That simply isn't what they're made of. They act like big, uncoordinated, leaderless mobs because they
are big, uncoordinated, leaderless mobs. There may or may not be a smaller core of people actually working well together within that mob. There may or may nor be a mission planner who launched the group toward one objective and made some attempt to coordinate their actions - but if there is, trust me, that's pretty much the extent of his ability to direct the action. Acting as Commander-in-Chief of all Bishop (or Rook, or Knight) Forces and coordinating multiple attacks at multiple enemy targets by large numbers of otherwise unaffiliated players simply is not within the capabilities offered by the game. It certainly isn't something the Mission tool allows anyone to do.