I'm Idio, not idiot!
Hey there, I'm Idio! Basically, I've been around Halo for a good long while, played all the games, read the books, know the community, and most importantly of all I can aim a BR at someones head if required. I find Halo fascinating, and if there's one thing in the world that I'm able to say I nerd out over it'd have to be Halo. The gameplay, lore, soundtrack, and community have kept me on board the series for over a decade, and as Sergeant Johnson once said, I'm most certainly the "hardest of the hardcore" of the Halo fan base. I'm a speed runner, LASO go'er, avid forger, Slayer when needed, support whenever, and I will shoot and scoot 'till I keel over-- so I'd suggest shooting at me first. Past all that though I am currently working as an editor for //REDACTED//, Lead Playtester for Sins of the Prophets, as well as being the community manager for Phoenix of War, and Blades & Roses.
This is an issue with base Sins, though we have been attempting to resolve the issue through some internal changes. We know about the issue, though as it stands there's not much we can do about it. It just happens sometimes.
Unfortunately we cannot dictate what the AI does, as it's all hard-coded into the game, and we can't touch it. We can influence them by changing prices on ships and structures, changing ship class roles, and putting research into the tech tree that players cannot get, but otherwise we're unable to do anything that would tell the AI "Hey, do something instead of sit around all match!"
Some of the issue comes with the way Titans work, some of it comes from buff changes that we have made - the issue may be partially resolved in the next release, though it is ongoing development trying to figure out a 100% solution eventually.
If you could possibly provide a screenshot, that would help.
What is your screen resolution, and what resolution do you have the game running at? This doesn't sound like a SotP related issue, though I'll be happy to help as much as I can. We haven't had any bugs like this reported internally.
It wouldn't really be worth it, because as I said, when the MAC is put onto a ability there's a lot of issues with the way the ability fires, and it's not really worth it. Plus, lower skilled players would have issues micromanaging fleets of hundreds of ships, manually dictating which ships should be firing, when the system in place is less micro, and more meta style fighting.
I'm heavy into economy throughout any given match, and having a strong economy in Sins also means you typically can have a pretty powerful military in the mid-late game, but you're weak for rushes early-mid match, so you've got a bad Achilles Heel when that's your focus.
It works for me though, because if you're smart about it you can turtle for a while, while your economy bubble builds up.
The way to do it is to have a very small initial fleet that is all about fast and efficient expansion, that can take early game unoccupied worlds very quickly, that you can then bolster with upgrades that will boost your economy, like better population centers. This small fleet means you're not really going to be able to defend yourself outside of tactical structures like MAC/Hangers/Patrol Stations, and so when you're on the defense (which you will be) you need to be focusing partially on turtle-ling either some of your inner colonies so you don't get completely swept over, or building a good external defense line on some of your key boarder worlds where you can push an enemy to attack you at.
Basically, don't get any fleet upgrade until you hit the point where you absolutely need a fleet, because fleet supply upgrades (not capital ship slots, but fleet supply specifically) eat away at your economy, as there's a meta surrounding it where you now have to actually monetarily and resource-wise supply your fleet. At later upgrades you might be eating away 50 - 70% of your potential economy just to have a larger fleet, and you might not actually need that larger fleet because you're just focusing on tech early game, unless you're being rushed.
Pushing the civilian tech tree forward, building trade stations, resource extractors, upgrading your planet population upgrades, and making sure every planet has a resource boost structure like a Springhill helps massively push your economy upwards. By the time you're entering the end game your enemies may be spending everything they have to fight you, while you have strong defenses that they can't push through, and you can pump ships out that are fully upgraded because you've had the resources to upgrade a build ships the whole match.
This strategy works for me pretty well, but as I said before, it leaves you weak early - mid match, and you can definitely get trashed by even moderately sized fleets if you're not ready, because you really don't have a major force to defend yourself until late game.
MACs already have a cooldown - there's generally a 60 second wait between volleys, depending on the ship. You'll notice this in large engagements, as there's waves of MAC rounds fired every so often opening up a new attack of Alpha Damage, which is what the UNSC is balanced around.
If we moved the MAC to an ability slot we would have a lot of issues, as we have done so in the past internally, some time ago, and there was a lot of problems with the way the ability fired off; not to mention we lose a potential unique ability in the process, for a lot of ships that could be cooler with something else as an ability.