Strength still decides a battle - there’s deliberately no surprise bonus. A fight resolves the same whether or not the defender saw it coming.
What intelligence changes is which battle you pick. A spy network shows you every province a country holds for six turns, so you hit where the garrison is actually thin and know a fort level before you commit, not after. A weaker power can win by only ever taking fights it’s already winning - it still can’t win one it would otherwise lose.
The better half: you can hide strength from the AI, but you can’t fake weakness. A province it has never seen doesn’t read as empty, it reads as the median of what it has seen elsewhere - so bait doesn’t work on it. Starving it of information does.
Fair warning: right now information is worth more than it should be, because the AI is held to the fog but its model was trained on worlds where it could see everything. That gets retrained next.