Welcome on the forum cthulhu. The AI will be upgraded in Dominions 3. Large maps with 10+ AIs on the hardest setting will give you some challenge, trust me.
Also with modding its possible to make the AI uber strong in a total conversion mod. [Example: give them stronger units for the same resource cost, cheaper national spells etc.] Anyways maybe it won't be needed at all, since the AI will be much better.