I've been playing campaign mode for a while (~30 campaigns) and while I enjoy the matches I think there is a fundamental problem - Instead of killing the enemy brain you can storm the map with Anti-air and heavy units, and continue on with your gold digging and gain thousands of gold that give you an unfair advantage in the following matches.
This is bad, because if you can pull this off at one of the first matches the entire game is sold.

I think a trivial fix would be something like AI brain suiciding when it's losing, forcing the opposite player to win.

I do agree, it's rather unfortunate really. I think there is something in place where the AI will evacuate it's brain if it detects it is losing, but I'm not actually certain that's a thing because I have never once seen that happen. To prevent just covering the map in units and killing the brain when it lands every time it might also be nice if all units that aren't in deployments are refunded when round is finished? But I'm almost certain that would have a lot of unpleasant side effects too, so probably not a good fix.

I'm pretty sure having the AI evacuate would be very hard in most maps. Rockets can barely lands properly if not on leveled terrain, and dropships tend to be easy targets for the AA Drone.

The real solution would be teaching the AI to throw kamikaze rockets/dropships like the player does (at least in the hard-nuts! difficulty range).

Or hopefuly this will be enough.

EDIT:

I also remember that some guy once did an overhaul for the campaign that did an interesting change, everytime before sending the brain in, there would be a barrage of standard bombs hitting the landing zone, so that it would be cleared (hopefuly) in order to make a safer entrance. That could be a good change IMO. The additional troops sent in now are good, but not enough.

As I see it you have a few different options;

1. Reduce the amount of gold on campaign maps to more reasonable/less abusable amounts
2. Make it so that gold mined during a mission must be sent back to orbit somehow before it can be used for campaign funds (increasing effort required)
3. Siphon off a significant portion of all gold mined during a mission afterwards; gold mined on-site can be used for that mission but too much excess is shuffled off to some kind of reserve (perhaps automatically converted into brains)

Option 3 would be good. I think that's probably the most fair and "simple" to do. Preventing rocket sniping and getting excess AA Drones is much harder to control, so limiting gold flow that way would be helpful.

Another option I think of is that most CPU drops should be done via Drop Crate to prevent the abuse of AA Drones and the like. They are harder to hit and are much cheaper, so that would give the AI an advantage that players already have and use frequently.

The issue I can see with #3 is that if you convert it to brains, you still have the same problem, just even worse since brains are more of a limited resource than gold. Otherwise, yeah, if you only get 10% of the gold you mine or something that would work.

Good point on drop crates. Maybe also just making aa drone more expensive but making the one you get in the dropship free would help?

Right, but having too many brains isn't really an imbalancing thing.

Also, problem with basic drop crates is that they can easily get embedded in soft terrain (snow, sand) which can mess up actor deployment. They'd need some tweaking.

Alternately, faction-specific or at the very least a good generic drop pod would be pretty neat. Maybe with some braking/stabilizers so the pod can slow down before landing (less risk of terrain embedding).

Yeah it is. Brains are the only limited resource in the game, your number of them determines winning or losing. They're also one-way convertible to gold so as long as you have brains you can't run out of that either. If the gold you mine gets converted to brains, you can just do the same mining forever business and then instead of having too much money like you do now, you can spend the rest of the metagame essentially godmoding cause you have a ridiculous number of brains.

So yeah, being able to replenish the only limited, victor/loss-determining resource in a way that strongly favours the player seems to me like it would definitely imbalance the game.

I suppose so. But even then, between the fund siphoning and the conversion-to-brains, it should effectively discourage the tactic- but also leave it open as an option for players who are strapped for brains. You could tie it to some absurdly high amount like 10k per brain or something.

Yeah, if it was put that high I guess it would work okay, there's only so much gold in each map. Siphoning without conversion to brains would probably also be fine, but I guess it doesn't make much difference with such a bad conversion rate.

I like the idea of bombs being dropped.

I think a lot of the problem is that the AI are just too easy to fool...

They have serious issues getting unstuck. They don't move out in groups. They don't squeeze off some suppressing fire shots. They don't predict ambushes well until you already have the first shot on them. They pause when you break their primary. They don't 'see' bombs or mines, so they just walk into them. They aren't vigilant enough with drop ships (crushing and abducting is powerful).

As for mining too much gold, why not just simulate all the time the enemy brain has as 'AI gold mining time' which is more or less close to the average a human could collect - and then provide an option when you're choosing to attack for a number of different airstrikes. The most expensive of which could even include bunker busters of some sort. Major's Ul-Tex mod has some sexy bombs that could make the game much more difficult to defend against. For example, you could order a bomb strike with varied bombs before landing - and so could the AI. Hell, make it so you can order more than 1 airstrike, even.

There's even a fairly balanced and relatively lag-free nuke mod (aside from the cost which I'd consider too inexpensive). It would be awesome to see something like that in campaign.

The only drawback is that this adds some randomness which AFAIK some people don't like - but it will force new strategies. *shrug*

On top of all of that, it would be cool to see the AI recognize when dropping bombs may be a good move and actually order, for example, drop crates to fall on your brain, or drop ships to drop a load of bombs. Or like attempt to crush or abduct troops. I have that much faith in the Data Realms devs

Meh, while there are some blatent exploits that completely wreck the ai (they don't recognize a hole in the bottom of the map as a hazard. there will always be exploits to beat them. furthermore making the AI smarter will only force players to come up with more convoluted and nonstandard exploits to win. Try winning without shooting around corners, or sniping from beyond line of sight. you'll find that the computer is fast to look fast to shoot, and a really good shot MOST of the time.

I actually am not sure where I was going with this post...
I was thinking to myself how the AI in strategy games is usually a blatent cheater as the difficulty goes up, researching quicker, building faster, ignoring resources, maphacking, ect.

I'm afraid I'm going to have to rain on your parade, then; they have a rule about the AI not airdropping munitions, and I think just using drop crates as bombs skims close enough to the line that they won't do it. arkman is right in that that kind of logic simply leads to an abusive cycle of escalating exploiting. It's much better to go in and find other solutions that aren't considered exploits or unfair, or find other ways to reduce the effectiveness of AA and so on.

What I can say is there might be interesting things in store for the AI soon, but I'm pretty sure I'm not allowed to talk about them.

Why not include it as a difficulty setting though? I mean, unless there's some way to stop players from exploiting those things. I mean even some things a player can do as simple as shooting through scrap/grass/snow is borderline exploitation. All the AI does current is throw more MOs into a scene which doesn't really add difficulty - it just forces players to abuse their weaknesses like not being able to see bombs or ambushes and take action. Plus that feels cheated.. if instead they had an actual gold limitation based on either the map's gold content, or more simply just an average rate that is balanced to what a player can manage to collect, it would give the AI the ability to burst down units when attacking as a legit strategy, instead of just kind of lazily and 'one-by-one' easy mode like they do now.

Sadly I had more written but the browser crashed, so sorry for the lack of punctuation. I touched a bit more on what could maybe be done about the way AI 'see's terrain though. For example, they never tunnel into a brain room even though a tech like Techion could nanolyze through terrain while covering the guy that's tunneling and stuff. It would be cool to see the AI 'see' that they may save time and have less risk of dying by doing this. Also for other/most factions, having a loose grouping of units instead of a bunch when they spot an enemy, because bunching up makes them more susceptible to splash damage and bombs..

Last I checked the AI will try to dig into bunkers and breach that way if it can. Actors need to be equipped with diggers, and then it needs to evaluate if it's worth the time or not - but it can happen. It may be game-mode dependent or it may have been disabled again, though.