It’s certainly good that the angels are an illusion, but there’s a catch. When the battle ends, the Angels disappear. So, when I see that I’m losing, I try to kill as many enemies as I can (without touching the illusions). Sometimes, I manage to kill everyone except the illusions. And then they disappear, and that’s it. No one wins. It’s a draw.
Let them disappear... but on the battlefield, they provide significant reinforcement. And in many cases, it’s decisive. Because sometimes, you only need a few more units to win. Haven can afford them, and Sylvan can too. Let them disappear at the end; it doesn’t matter anymore. But they will do their job.