[SelfishGene]

I've lost even moderately powerful, borderline thug/SCs to random AI armies, if they just happen to have the right casters or right units.

There are a few situations where fighting the AI is hard, but the main ones are when you take sleeping/imprisoned Pretenders, non-combat Pretenders, vs. water nations (or vice versa for EA water) and/or sloth scales. To fight effectively vs. the AI's masses of chaff you need either efficient, high resource units, or some force multiplying units like spell casters ect. Unlike in multiplayer the AI is suicidally aggressive and there are no negotiations or alliances till the end. And even good players might have a tough time getting into the water vs. the AI if you haven't got an easy route to good water strategies.

You can make the AI reasonably difficult by building your nation thematically, btw. Rainbow pretenders et al are great for the end game but don't do you much good if you're getting thrashed at turn 15 by huge waves of chaff.

Honestly, though, the AI seems somewhat .... variable, as to it's effectiveness, as well. Some games, it's like i outbuild them 3:1 and crush them easily on the harder levels, even if i take time to pause between provinces to raise dead. Other games my 3-sloth Tir gets swamped by enormous numbers of chaff, and if the map is shaped in just such a way, 4 thugs might be holding them back at four provinces, but then the AI always seems to find a way to break through somewhere else and progress is very difficult. Generally though i do poorly vs. the AI with sloth/low resource national troops/thematic Pretenders, and beat them easily with prod/high resource national troops/SC Pretenders.