In mission 5 of the ARM campaign, it became very noticeable that the AI can attack me from far beyond my visual range. This was very, very irritating and unfun but hardly made the mission impossible.

Then in mission 6 it became maddeningly irritating, as the AI is no longer using this to attack only my units from far away but actually destroying my buildings which I'm not sure any of their units have ever been close enough to even see.

I'd like help, but I simply hate this dynamic which seems unavoidable in the single player game. Yet I have very much liked the game other than this and want to play through the missions. Does anyone have some sort of solution other than "just bite the bullet or don't play the missions"? Am I somehow doing something wrong? Is this just part of a fine game and I'm weird for hating it?

Use your radar to locate them. If you decide to build plasma batteries instead of a navy, you'll need to manually target using the minimap.

Mission 6 is particularly tricky because you're having to set up a naval base under fire. Use your commander to reclaim wrecks where possible, and clear the entrance to the bay with submarines at the earliest opportunity.

PS: at the beginning, clear all the enemy AKs from the island, and build a pair of solar collectors before capturing the enemy metal extractors. Then go for either a shipyard or kbot lab depending on which approach you prefer (offensive with submarines, defensive with plasma batteries\laser towers).

Well it seems skirmish mode allows adjusting the fog of war. Setting it to Dune2/C&C style would make the AI's seeming disregard for the fog of war more tolerable since it would no longer be totally cheap, but I can find no way to apply it to the missions.

As I said, manually target weapons using the radar minimap. Alternatively, use scout patrols.

You can use the targeting facility to avoid micromanaging in some missions and skirmish\MP but you still need radar coverage (and a fusion reactor to power it).

And as I said:
"This was very, very irritating and unfun but hardly made the mission impossible."
"it became maddeningly irritating" (Note that I did not say it became "hard" or "impossible".)
"I simply hate this dynamic"
"Does anyone have some sort of solution other than "just bite the bullet""

I never said the problem was the lack of a walkthrough. The problem is I find the AI's cheapness in regards to its seeming disregard for the fog of war unfun. Unfun, not hard. I know the game can be still played despite this, my problem is I don't find doing so fun.

What I can take from your posts is the strong suggestion that the AI is simply broken this way and there is nothing I can do about it except bite the bullet or not play the missions.

In this particular mission there are already AI units there on the island to begin with. In my experience the destroyers that attack will close to visual range at least some of the time. Also, the AI missile ships have radar - its perfectly legit for them to be sitting there spotting for the other units.

I can open up the mission in the editor to see what commands the enemy units have if that helps?

It's been said in the thread, but in TA the rule of the game is radar coverage. If you got it, you exploit that advantage. The CPU player has a couple units with radar in range of you, and is just shelling you at random. I do it all the time in my games. If you tell your artillery units to fire at will they will open fire on anything in range, regardless of LOS.

Your best bet is to get some scout plans up, find its radar, and take it out. After you do this you should be all set. It'll be a bit of a pain in the ass to get yourself up to the level where you can take out the enemy radar, but it's necessary.