Oh, uh… that hadn’t occurred to me. I had only ever tested against my own defense team and then assumed AI was switching because it was my team.
But it seems like you are right, if the other Choose One troops work like Wand of Stars. I just tried it in Casual PVP and the AI consistently picked the same spell as my last cast. Yikes.
EDIT: I tried testing a little with some Vulpacea troops in a mirror battle. The AI seems to choose for itself.
For example, I couldn’t get the AI to choose Fenix’s 2nd spell (summon troop) by changing which spell I choose for Fenix. Even when the AI had an empty spot, it choose damage once when my last Fenix choice was summon.
Same for Vulpphire Hunter. It seemed to choose randomly in some way which damage spell it used.