This. My personal favorite game for co-op vs the AI was RUSE - they had several different AI profiles that tended towards certain strategies you could specify, or it would choose at random. However, it really did respond to what units you built and what strategies you chose, building bunkers against a rush and such, or building a ton of anti-tank weapons if it saw you had tanks.
This meant that subterfuge and concealing your intentions was legitimately a huge part of the strategy - if you intentionally let the AI see a lot of a certain kind of unit and then build a different kind of strategy, you'd often see success, but because of the way the AI strategised it could sometimes meet you head on with an unexpected surge because it briefly saw you building up from an unspotted recon unit hiding somewhere.
Ultimately it is relatively easy to defeat with a little experience, but I still several years later occasionally boot it up with a friend to try and beat the hard AI 2v4 - we've only managed a handful of times, and the experience of slowly being whittled down back to back is a great experience to have in a friendship