I don't really see a problem beating any AI, actually in the old days I've gone for solo against 3 normal or solo against 2 insane AIs, oh well. And the tactic is kinda simple, rush most expensive units.
I usually play Undead/Orc, where I either go for Frost Wyrm + Necromancer or Wind Rider + Shamans. Basically, full DPS build.
And when did you wake up exactly? That's something I used to do when I began playing the game and believe me it never works. So you'v beaten 2 insanes in a team by 'rushing' frost wyrms... people these days.
I beat insane undead by use of sorceres's polymorph on abominations and frost wyrms and roughly 5-7 priests with inner fire toggled and switching it to heal after the fast buff. People tend to try using dragon hawks but you might notice the moment you cast the aeral net disable the AI will focus them and burn them down very fast.
Tanks are bad against frost wyrms because of their 2 second cooldown on the barrage and focus they recieve from siege units, the high costs and limit they take. Also their disability to stay healthy without a few peaseants runing behind them to repair like lunatics. They are good against the mid-tier flyers like gargoyles, dragonhawks, batriders etc.
My strategy against AI is to take advantage of it's weak spots :
1. The AI tends to waste town portal when a single unit attacks his main base/expansion. Easily at starting stages you send a single unit against an expansion and force the AI to use town portal there(and he will!) then go inside his main base quickly and wreack as much havock as you can. If the AI already got flyers - e.g. we are talking about undead so gargoyles - they tend to run infront of the main army when retreating to defend their base. Just expect them to arrive first and get them as they do.
In best case scenario they won't even reach Frost wyrm phase. That strategy works on some of the maps where expansions are a bit go-around from the main base. The time period ofcorse shortens graduately.
p.s. Blood Mage's banish with 2 sec. cd is a must when dealing with t3 units. Also good mix is the holy light and storm bolt on a banished target but thats highly unlikely to happen, I mean reaching 3 lvl 6 heroes. Games should end faster than that.