The vanilla AI is a one-trick pony. Or rather, very limited tricks. Eventually you get feel for it and start beating it regularly (not knocking it, its still good enough to provide an opponent for most of the long learning curve)
But there are mods and maps designed to boost the AI. And program generators such as SemiRandom or Chaos. You tend to have to find the threads talking about it since its a different course than the "fixing" or "balancing" ones.
Personally, my favorites for "more more more" unbalance for solo play are Worthy Heroes and Epic Heroes (to get more heroes), Mytheology and Immortal Pretender mods (for more pretenders), the More Magic SItes mod, CPCS (more summons), SingleAge (more nations), and Streamers & Standards because the flags got old to look at. Also Amos modded nations make for new exciting AIs.
If those get old you can always join a multiplayer game with specifically boosted AIs
