There's a big difference between a balancing issue and broken game design. You can't just conflate the two so brazenly.
In fact, assuming that it's one of the two implementations I suggested above I see it as adding an interesting gameplay choice for the player (who to use in the drills each week) and working to partially rectify the balancing issue all in one fell swoop (greatly reducing the amount of XP available to the user team which the CPU never has an opportunity to receive).