There is nothing balanced or realistic about the current coalition dynamics.
Let's start with history. The first major peace of the EU era, The Peace of Thorn, involved Poland taking four provinces from the Tuetonic Order. If you load up the history database during the war, Poland has no claims nor any AE reductions. Doing this historical peace gives you a wildly ahistorical outcome - Poland ending up facing a coalition against everyone to whom it is not allied; in reality the Teutonic Order withdrew from Polish politics and nobody else gave a damn about Polish expansion. Well what else? Well in 1453-1463 the Ottoman Empire annexed (with no claims, except maybe one): Constantinople, Morea, Athens, most of Bosnia, and most of Serbia. You can also arguably through in vassalizations of Wallachia and Moldavia. The coalition from that tends to involve just about every Christian remotely nearby. Who went into coalition against the Ottoman Empire - at worst Hungary and maybe a few merchant states. Well what about the Italian Wars? Well the League of Venice formed before France took any territory and after all did so as a result of France accepting a throne claim against an excommunicated monarch. Following the initial war, France took out all of Milan (something like 100 AE) and nobody did anything for a quarter of a century. Spain, of course deposed the Neapolitan King and directly conquered the place, and no coalitions formed. The Muscovite Lithuanian wars? Enough AE to put every Catholic on the Russian borders into an alliance somehow resulted in precisely nothing like a coalition against Muscovy. And I can go on, and on, and on. War of Spanish Succession, the Napoleonic Wars, the Mughal Conquests, etc. All of this is utterly ahistorical, pretty much every historical peace was either status quo ante bellum ... or involved more land changing hands than you can do without tripping long lasting coalitions in EUIV.
But what about balance? Don't make me laugh. Is it balanced that Trier taking two provinces is deemed as more of a threat to the HRE than the OE Bosnia, Iraq, and Kaffa? Or that if I get detected fabricating a claim (something done routinely throughout the era, by everyone) it has a bigger malus than actually territory in some situations. Or that landlocked countries are utterly and totally screwed compared to people who can hit Muslims, Christians, and maybe even Eastern Religions and Pagans. Or consider the risk/reward. You beat a coalition consisting of France, Sweden, Spain, England, and Austria, your "balanced" reward is less than you can manage just against Russia alone. Or somehow it is "balanced" that the magical AE timer trumps every single other strategic consideration ... please - Sweden is going through a peasant's war with some pretender rebels running around with Russian troops invading Finland. Should I invade and take their Baltic coast or not? Nope, I'm too close to the AE threshold. It is less expensive and a far better choice to wait 10 years, let Sweden rebuild its army and then invade for two province than to hit them when they are weak. The balance between AE and every other strategic concern in the game tips to AE in 95% of cases or more.
And that accomplishes what? Money is pretty much worthless once you become a major power and start efficiently using mercs. Trade power is a joke, it gives you money - if you are actually in a position to capitalize it might be worth something, but it is dead in 5 years. But don't I actually hurt my enemies? Well you can burn their manpower pool and force up their WE ... but I have found that I lose more troops to rebels than I kill of the enemy. Worse if you do start nuking the AI bad with low manpower and and high WE, then you can break them back to 0 stab and gift them a bunch of troops thanks to a bunch of big rebel spawns.
In short about the only thing worth anything for such an AE-less war is sinking ships ... but that is also what you can do when you declare war anyways. And of course, these being your rivals, you pretty much can't keep them out of the coalitions: -50 rival, -25 competing superpower, -15 declared war, pretty much alone will drive any rival with any AE into coalition. Add in the normal crap - Border friction, has claim, has CB, wrong religion, allied to rival, wants my provinces, conquered province same religion, and of course the AE relations hit itself. Going to war with your rivals for trivial amounts of gold (either directly or via trade power) is so totally not worth it. If your rivals, by some small miracle, aren't already in a coalition, they will be heading there shortly thanks to your war nuking relations further. If they are already in a coalition, good luck with that "trade power" and cash thing, you can either wait for the war score timer to tick up to 25% and then farm battles or actually go siege places (like 20) and wait for the coalition to realize that it has been beaten.
I mean, if the game gave me anything useful for 0 AE, it would be one thing, but for any real war your cost/benefit ratio is utter crap for anything but returning cores or releasing nations. This, of course, requires vassals with old cores on the land in question, but of course many places lack such cores and over half of those expire in the first half of the game.
I'm very interested in hearing why people enjoy coalitions - particularly as there are millions of balanced and historical ways to improve the mechanism. But so far most of this is from stuff that doesn't hinge on coalitions (they actually don't declare on you if you are sufficiently stronger, and strong alliances behave quite similarly) or stuff that is just downright wrong.
