There is a way to sort of split them. It comes down to which AI pack you allocate to the AI players.
You have three choices if you haven’t installed any data packs.
CD AI, HD AI and DE AI. The DE AI option is the new AI that comes with the DE upgrade. CD AI is the original AI that came with the first expansion way back when, and HD AI is as it says, it’s the AI that came with the HD upgrade.
The easiest AI is the CD AI, even on HARD it is fairly easy to defeat if you are a relatively competent player and know some basic build orders. The HD AI is a little tougher, just keep in mind the jump from Standard to Medium is quiet big in difficulty.
The DE AI is the most consistent and balanced of the three, the moderate difficulty would be equivalent to a 600 Elo player or there about, the HARD level on the DE AI is a challenge if you are a novice player but if you know how the AI “thinks” then it is reasonably easy to beat. Hardest and up is fairly difficult for anyone other than regular players that have a good understanding of build orders, tactics and counters.
Hope this helps.