It's not that simple. When a player switches sides, they can easily start viewing the side they are no longer playing as the enemy. However, if they had to play for both sides simultaneously, that would be a different story.
Added 1 minute later
But the computer is just brute-forcing its way through. This means that the side with greater raw power will win, rather than the side with greater tactical potential.
Added 2 minutes later
Paladin and Archangel is a very useful combination, for example, like Fury and Rider in the Shadow League. The whole point is that Paladins attack everything, preferably from a distance, and Archangels resurrect. The "Divine Might" spell would be very useful, or whatever it's called.