Your OP sort of has the issue written right into it. For games like CLoD or the new Battle of Stalingrad, or the DCS series, to have 500 people, IS the entire issue right there. According to HT, who I believe is 100% right, and knows more than any of us here, making a sim with the level of detail and the way these other sims work, as well as having an environment large enough for 500 players, would require defense department levels of computing power. It's sort of one or the other, at least that's how it's been explained to me.
That said, there IS a lot of gaming/fun value to be had in these other types of games/sims. They certainly are NOT the AH experience, but for smaller group multiplayer or single player, they can be fantastic. I have pretty much all the DCS, and they are complex enough that I'm only now just getting to the A10C module after flying BS and FC3 for a year now, as well as messing about with the 1/2 done F86 and the excellent Mig21. They are more the thinking man's type of sim, what everyone dreamed of someday having back in the Microprose flight sim days. Don't get me wrong, the multiplayer can be great, I'll post some links to some FC3 multi player squad videos at the bottom. FC3 is a great way to start, as it isn't quite as complex as the other modules. That said, the F15C stand alone module comes free with FC3, and has a little more complexity, FM, avionics, and such put into it. Good news is that they did the same thing with the SU27 just days ago, and included it as a free upgrade to FC3 owners, so you don't need to buy the F15C or SU27 modules if you buy FC3 now, which again, makes it by far the best starting up module IMO.
CloD and BoS are sort of a middle ground, not quite as complex as some of the DCS modules, but more so than AH. So far as the flight models, I'm the wrong person to ask, but I would say just by feel,look, and experience, that they are reasonably close to what AH offers, close enough for the non pilot gamer like myself to be happy. There is a large community of multiplayer people, but it isn't nearly the AH experience as stated already, but it can still be alright for a diversion. Personally, I like them for small multi, as in 2v2 or you and a good pal playing vs the computer AI or whatever. The single player campaigns are good as well IMO, although not without controversy right now with BoS what with their unlock goofiness, but even still, it's pretty good.
One thing you should check out is Falcom BMS. If you can get a hold of an old original copy of Falcon (easy and cheap), the BMS is free, and it's insane IMO, even more complex than DCS, with a HUGE community to help you (easy to find help videos on Youtube for example and such). The dynamic campaign - there is still nothing out there like it, and you can fight in several wars in different times and places, and have yourself a months or year long game on the strat end vs the AI. The graphics are dated - it's a lot like AH in same ways, in that the gameplay, idea, and original concept are SO good that 16 years later it's still the only game in town for some stuff, and very popular.
Make sure to put these in 1080p on youtube. Do some searching of your own as well, there are tons of DCS, CloD, and BoS vids out there.
https://www.youtube.com/watch?v=w2iNn54qlBshttps://www.youtube.com/watch?v=NkX5emat5doSome Falcon BMS
https://www.youtube.com/watch?v=Y_NWPf7MOIQhttps://www.youtube.com/watch?v=uU3pmXvnc0khttps://www.youtube.com/watch?v=Qhl7e4xoF2E
