The fundamental issue with making a “more fun version” of the faction war is that because of how every other threat is also treated, it needs to be serious.
Dark Portal opens again and spills demons from Outland? Rally your forces, Horde and Alliance! The Argent Dawn is fighting for the sake of our world, and you just got drafted to invade an alien world!!
Scourge invade from Northrend? Put aside your petty grievances, because all life is under threat!! It’s literal zombie apocalypse time, and you need to save the world!!
Deathwing awakens? Holy crap, this one might actually do it because he already started the job!!
Dark Portal opens again and technologically advanced orcs invade? We’re all gonna die, go through and invade yet another alien world, but it’s kinda that first one too, and stop this threat to our very existence!!!
Demons are raining down from the sky itself!! WFT?!? This might really be the end boys!! Throw everything you possibly have at it, because we have next to no freaking chance again!!!
Ok, freaking N’zoth now?!? He’s literally eating the soul of the world!! We can’t, we just cannot possibly win this freaking thing!!! Do the best you can, because nothing can be worse than this!!!
It’s worse now!!! Totally worse!!! Death itself is coming to kill us all!! AND the Scourge are back, freaking hell!!!
Ahem.
Literally every threat is an extinction-level threat. Every single time we’re called to act, it’s for the fate of life itself, so the very idea that the only two megapowers who are barely holding things together just decided to throw down against each other? It has to be at that same scale, or it’s just as dissonant.
Because if it’s not, then it means everyone’s a freaking idiot. With annual threats looking to wipe everyone from the face of the world, y’all thought it would be a good idea to weaken each other in the few moments of peace and safety we have?!?
The problem is that because everything around the factions is some life-or-death-but-probably-death struggle against all odds, the very idea these two entities would fight each other in the middle of it all is beyond ridiculous. The over-the-top level of threats regularly facing Azeroth shouldn’t leave any room at all for a blow-up between the Alliance and Horde.
And yet, there’s always room for mass-slaughter of the only line of defense we have against the infinite cosmic threats facing all life.