Having browsed through most of this monster thread, I see lots of good points. I had no idea the situation was so bad. I played WarBirds a lot, then continuing with AH for a couple of years. Then nothing for half a century it seems, and I have been lurking/playing AHIII since early beta. The whole idea of this game is fun, online fun. What is fun? who knows? there is no precise definition. But - when people keep getting back to something, when they want more, you can bet it's because they want more fun. Likewise, when people leave, it's because the fun has gone. Pure and simple, there is no other way to explain this for a game.
What is fun for a "wolf", obviously isn't all that fun for a "sheep". The wolf likes to kill the sheep, the sheep likes to conquer bases without getting killed by the wolves. They all pay the same amount. But when the sheep outnumber the wolfs 10 to 1, you better look after the sheep, because 10 sheep brings in more money in than 1 wolf. Well in WB we had "Otto" firing the guns on bombers. Otto did a good job, and you had to be a really good wolf to gun down a B-17. 2-3 bombers in formation, almost impossible, and with a couple of fighter escorts, forget it. By the time you had gunned down the escort, you had no ammo left, or had dropped so much in alt, that you had no fuel left to catch up to the bombers. Simply put, you couldn't do it unless you were 2-3 wolfs together. In AH I can take a 3 ship B-29 and be shut straight down by a lurking 262 shooting from 1.5 k behind. Otto would converge all the rounds to the target, in AH the guns from a bomber converges where exactly? Maybe there is a way, cause I have met some bomber pilots that are really good at it, but how, and where can that information be found? Simply put: fun? - no.
Then there is the perk system, favorizing the best. I also want to fly the 262 every now and then, even if I'm no top fighter ace. Again fun? - no. WB had this rolling plane set, from early war to late war. That was fun, added a dimension. Always something to look forward to, added historical depth. From turn and burn to zoom and boom. Always looking forward to a few hours with the 262, still, what a relief and cool change when getting back to early war. And why not go further, into early jet age?
Also radar alt should be terrain oriented, or at least increased to 200' or whatever. It adds more fun for more people.
Ok, so this won't explain the drop from 2009. I don't think anything fully will in any case. I see the younger people playing DCS and world of warplanes, both of them alternately. And everybody just has to admit, DCS is as amazing as WoW sucks. Then this IL-2 seems very popular also, maybe more so than WoW? + lots of other space/war sims. The younger generation haven't even heard of AH.
Back to the main point. Who cries the loudest? Is it the sheep? no, the sheep just quietly leave to whatever else is more fun. Is the the alpha wolves? no, the alpha wolves always remain alpha no matter what. They may leave though, but with style (quietly). The one who cries the loudest are the alpha wannabees. They cry out because they aren't good enough to get the kills they feel they deserve unless delivered on a silver platter.
Things has to be made so the sheep thrive, because they are many. So, it becomes a bit more difficult to kill one sheep, but since there are many of them, it doesn't really matter all that much. You have to pick out the weakest, instead of just the closest. The wannabees, they can go and play WoW if AH is too difficult.
Just my 2 cents
