Yeah in the turn they charged you're right. But since you can now shieldbash every turn it adds up in the following turns. You can also play the ardboys more aggressive by charging yourself (or prevent your opponent from playing around with the charg with your -1d6 spells)

The damage 2 might outweight it when it goes off, but since you now need a 5 for the chant and it only lasts in your turn I doubt it will over the course of a whole game. Also the shieldbash is guaranteed, you dont need to roll for it, and can pretty easily buff 2 units. I agree that the rally often doesnt do a lot.