Talking only of standard, base game vehicles and radar mechanics, Anti-Air SPAAG vehicles are completely useless against a competent attack helicopter crew. Tactics and integrated air defense networks aside, the standard AA vehicle is entirely unable to effectively accomplish its role of protecting armored assets from air targets reliably. Due to the fact that I predominantly play KOTH I know I'm probably going to get a bunch of people in here telling me to play a real game mode but my point is about the BASE VEHICLES, not the gamemode in which they are used, and I'd like the responses to be limited to that context as well.
Arma is a game that prides itself on its realism of combat systems. However the AA problem is a glaring deficiency in what I consider to be an otherwise outstanding game. My main points of contention come from a few simple facts about the imbalances between ground AA and air assets with guided missiles and radar. They are:
1) Radar and spotting ground vs air
It is significantly easier to spot ground targets from the air with radar vs spotting air targets from ground radar. This is simply because the radar mechanics in arma are on a 2D plane with only flat distance information given. In a helicopter this is perfectly fine as the ground is also a flat plane, you simply look along that plane at the specific distance and heading and find your target immediately. On the ground, it is a different story. The helicopter could be 4KM away and 4km up, or flying nap of the earth, or anywhere in between. Finding the altitude of a helicopter at max distance is a process that takes time that an AA vehicle doesn't have to spare, while the helo, given that it is finding targets on a 2D plane instead of a 3D space, doesn't have to deal with it. It is mathematically easier, and when trying to contest good helicopter pilots it is a significant disadvantage when seconds count.
2) Countermeasure systems
Helicopter countermeasures are extremely effective at range. I don't know the exact percentages but firing all 4 titan missiles at a helicopter and not hitting a single one is not an uncommon occurrence (and yes I've tried a bunch of different strategies for shooting missiles at helicopters). Flares do not impede the helicopter from continuing active fire, do not have an activation cooldown between uses, do not have as limited number of uses vs smoke, nor do they require an extra player in the vehicle to activate. Smoke denies the ground vehicle the ability to continue return fire, limits its location to within the smoke preventing relocation, has a cooldown between uses, has a much more limited number of uses, and requires an extra player in the vehicle besides the driver/gunner. While none of this is directly related to the primary issue of helicopters vs AA vehicles, I figured it was worth showing another series of inequalities in defensive options.
3) Ranges and and weapon systems
Now for the meat of the argument. The AA vehicles cannot contest helicopters with their weapons unless the pilot makes a mistake (read: is a noob). I know the counterargument for some of this is going to be 'ITS JUST A GAME' but if we are striving for a realistic environment it needs to be said. AA vehicle-based weaponry should outrange helicopter weapons, period end of story. The fact that the most common (and effective) tactic is to fly at max altitude and rain ATGMs on anything with a radar signature is ridiculous for a helicopter to be able to do in a radar-based ADN environment. IRL if you were in a helicopter doing that in the vicinity of a dedicated radar AA platform you would be obliterated in the time it takes to fire the missile. Right now the primary target of AA vehicles (THE HELICOPTER) outmatches it so completely, it is never worth it to buy an AA vehicle to shoot it out of the sky. Guns are not auto tracked (like we have now irl, let alone 25 years in the future) but manually aimed, they give you heading information but do not auto-range, and the damage they deal is incremental over time based on how often you score a hit (which if the helicopter is maneuvering at max range and altitude is hard to do consistently, call me a noob all you want but it is a hell of a lot easier to hit a slow moving tracked vehicle once than to hit a maneuvering helicopter multiple times).
Meanwhile the ATGM system on the helicopter needs to hit once (or in the case of DAGRs about 4 times but when fired in quick succession it functions the same) and you are instantly dead. You can pop smoke to avoid the auto targetting feature on the chopper but you don't have enough smoke on the vehicle to actually survive continued contact from even a single helicopter's payload outside of getting rearmed, and I have already described the deficiencies of the smoke defense in the above point. Titan missiles are not consistent with the countermeasure system and that is assuming you are alive for long enough when facing off against a helicopter to actually get a lock and use them all before needing to pop smoke and ruin your ability to fire effectively.
Damage, weapon systems, countermeasure systems and target tracking on ground based AA vehicles are all objectively worse than attack helicopters for the base vehicles. Yes, you can disable some of these features. Yes, you can mod them. But the fact remains that there is a vehicle in the game that is incapable of fulfilling its primary role (again, unless the pilot does something stupid but you can't plan for that) due to the mechanics of the game if all features are enabled.
In a vacuum, an AA vehicle in the open should be able to beat an attack helicopter in the open. The opposite is true as the game is now. There are a few fixes that could be implemented that could help address this issue:
1) Autotracking guns
We have them now, today. No AA piece is manually fired anymore unless you are subjected to HARM SEAD sorties which is not the case in the game for most multiplayer situations. Immediately getting a firing solution and gun lock on a helicopter would go a long way in terms of being able to instantly suppress the gunner and bring down a helicopter in the open.
2) Longer range locking missile
The primary weapon for most ground based AA vehicles that take on modern attack helicopters is a missile/radar system combo that outranges the ATGMs that helicopters bring. THATS WHY YOU TAKE THEM ON THE VEHICLE. They are big and accurate and can't be carried by people. Right now we have MANPADS strapped to the sides of this thing that are literally the same thing infantry carry and no better. The gun is worse and the missiles are too short range to effectively face off against a helicopter due to the countermeasures issue discussed earlier. If there was a missile that had a longer lock on range vs the attack helicopter ATGMs that would not only balance the gameplay against high-flying attack helicopters but also actually be realistic.
3) Missile less likely to be spoofed by countermeasures
Again, looking at what we have now in the military with combination IR/UV seeker heads, flare-based countermeasures should be way less effective than what they are now. If after all of the things I described in the engagements earlier don't come to pass and you actually do manage to get a lock and fire your weapons at a careless pilot, they probably won't hit if the enemy knows how to evade missiles. AA missiles (especially vehicle based variants!) should be a way bigger threat to helicopters if one gets launched at it and right now they aren't.
This lack of threat leads to specifically the gameplay strategy of staying at max altitude over the AO and being uncontested except by other helicopters, almost never by ground-based AA vehicles which SHOULD be the primary threat and concern for helicopter pilots. Instead, nap of the earth flight with limited radar visibility should be the norm as that would actually require a level of sneakiness and vulnerability that would be open to a lot more opportunities for engaging helicopters with other weapons, and also because that's how helicopters have to operate to stay alive in a contested AA zone.
TLDR: Please fix AA vehicles.
Also is this actually the right place to post this? If not let me know where it goes.