I have been having trouble beating standard/hard IG computer, the one with the SS AI 3.2 Dawn of Skirmish. The races and the reasons for having difficulty, I will list one by one.
Tau - Tau fw have a really short range, so need a spotter, which I use Stealthsuits which is fine, and keep out the sight radius of the Guards. That is fine and I can keep out of the ranges of the buildings guns as well, and with the IG turrets, I have 1 squad of meatshield kroot to take the dmg. But once the Command Squad comes along, my SS usually insta die, the kroot tie up the command squad, but then the Guards come along with nades and blast the hell out of me, and with FW set up time, I usually can't hit back, because the AI IG usually has 4 Guard squads and 3 nades each squad, so my kroot tie up Command Squad/ get blasted to hell by nades, so the kroot die, and my fw usually die as well due to command squad chasing/meeleing (sorry for spelling) a fw squad. I usually have a couple snare traps, but it doesn't slow them down as much. I get to T2 in about 5 -6 min, so I can get a squad of pathfinder, but they're stupid even with me clicking GET BACK GET BACK and die. Then my skyrays come out, that usually kills the Guards but still take a fair bit of dmg due to nades, and or the CS meeleing it, and usually sents come out and fry the 2 skyrays in no time. Even with DF, CS can spot it and insta die as well. And to add to the problem, HWT come out, outranging and outsighting FW and kroot can't really be the meatshield because they usually die one by one just to attack, and even with a barrage directly on it only about 1/2 of its health is gone, and that is only 1 HWT out of like 3...
But I can win if I kill every infantry but crawling forward, selecting each individual squad and barely staying out of range.
Eldar - Basically same as Tau, due to me using DR, but even worse because DR has shorter range, and the FS as the meele distracter. I use Physic Storm and Mind War, but Physic Storm, from my PoV, doesn't really do a lot of dmg? If I use Shees, even worse, because Shees usually have to close in, and in that time, usually half the squad is gone. And the building guns? I have to wait till Wraiths/ Falcons come out (5 -6 min) and take the dmg, but still, they lose a fair bit of health and may die as well. I have used Wraithtomb and that is good for turrets, but once I used it on the HQ buildings, the production stopped but the guns kept firing? And I was lucky that the IG had no sents.
Chaos/SM - CSM and Tacts can take the dmg dealt by the buildings for some time, and that is good, but 3 Guards with nades... murder them so easily, even if I have 4 CSM and a Lord, the AI can micro away so they can fire again/ near a LP/Turret/ or hide in buildings. I have to wait till Vehicles come out, and again I harrassed IG so much they were still in T1, they killed 3 of my Defilers just from maxing out the slots the the HQ and or the Infantry Command.
SoB - Not really a problem because once my squads have flamers, can break morale so easy, but still, murder to get them in range of the flamers, and I can use the Canosness's Purifying Light to maybe stop the building's gun firing (not sure about that)
Necrons - Don't really play much Crons, but still, nades flatten the Necron Warriors and that is pretty dmging even for Crons; and if I drop FL near them, they run away so fast the the FL can't catch them. And IG are hard to beat for Crons if the Lord doesn't have Solar Pulse.
So... that is the end of my rant about how OP IG are T1, T2, and I don't even want to think about T3 and T4...
Btw this is IG Standard/Hard so they don't really have a resource headstart