NARC/Tbolt: NARC sniping isn't all
that easy, though if you're sitting still you're asking for it. This particularly applies to AA running active radar while being stationary: as a Tbolter, my BHP lets me detect you 250m beyond where you can detect me, at which point I can line up a shot, choose to go passive on approach, etc. Also beware that AC fire streams tell me where you are so that even if I can't detect or see you, I can still aim at the muzzle flash and score hits. Use zoom x1 and scan the skies if you're running AA. If an Aero lines up on you, don't sit still unless you're sure you can down the Aero before he fires.
Aeros: Yes, landing is pretty tricky. A good AA will control the skies in a 1500m radius sphere around it, ignoring terrain obstructions. Keep in mind that fbombers must, if they want to go for a close high-percentage drop, come in low enough to be shot. Keep in mind that the red stars and boxes tend to more or less form a stream of reinforcements all the way back to defensive turrets, meaning usually that someone will be able to take a potshot at you. JJ's can be a good fbomb counter, if you happen to notice an fbomber approaching. LRMs are not good AA -- they are mostly just a nuisance to aeros, forcing them to spin around (nauseatingly) for a bit.
LBLs: I don't know how MW PvP LBL balance was, but I can tell you that I notice quite often the highest-scoring players on servers playing pretty much exclusively LBL Novacats, forsaking heavier chassis. Even on a hot map like Inferno.
Gauss: Limiting gauss ammo doesn't make sense to me from a physical perspective, as the weapon derives its power not from the weight of the round so much as from the speed at which the projectile travels. To make them less useful in-close, a moderate reduction to RoF would suffice, and perhaps be reasonable for long-range snipers to suffer. A less sensical but perhaps more entertaining solution might be to add a charge-up delay to the shot -- I would suggest something giving the target time to respond -- say, to mash
X -- except that with lag I would expect that even a one-second indicator would arrive at precisely the moment when the gauss round strikes your Mech. But perhaps that charge-up time would only compound lag-warp issues (particularly if they actually managed to change speed significantly in response).
LRM camping: I find it to be incredibly boring and rather ineffective against someone aware to their threat (other than preventing me from going certain places and fighting certain ways) -- but they are also easy to use and good against people who do
not really know how to avoid them. I speculate this causes newbie to join mod, get destroyed repeatedly by LRM campers, become an LRM camper themself, find this to be insanely boring and not at all what they were hoping for from the mod, and thus quit the mod. Though there may be some demoralizing effect in, say, being destroyed by a (more experienced) pilot while in an AA that is claimed to be overpowered -- but as they start to try to fly, they will consistently be destroyed by average AA. But I suppose that's a fundamental problem for any PvP game... shrug. Some way of knowing what the other player is doing that you are doing wrong (without wording it as such!) might help a lot. The "killcam" idea, I guess -- though how and in what form, I don't know. (Maybe loading screen tips?

With references to the wiki strategy articles???)
(
LRM PB: Maybe a minimum arming range on those LRMs? I don't know; allowing the PB LRM salvo has its pluses and minuses.)