Agreed, I feel like the behavior has regressed over time. I remember when the demo for LockOn came out where you fly iirc an SU27 against a Mirage after the merge and it was basically 50/50 whether I would beat him. He didn't extend ever and kept in a tight turn fight.
There's odd defensive behavior in enemy flights too, I just set up a quick dogfight my Su27 vs. two Expert Mirages. Only the flight leader would consistently drop flares, the wingman never dropped flares. Then the would extend away and just make a lazy orbit, then one would make a head on pass.
I wish the AI pilot would occasionally notice your IR missile launch and then just dump a load of flares. I wish excellent AI would also fire more than one missile at you.