Hmmm good queation: I would say not allow battle if the value is exceeding the limit.
Keep the battle button touchable/clickable, but once it is preassed, pop a big ass red message in the middle if the screen with the reason that player cannot battle: Your Power Score exceeds the maximum allowed for your level. Please reduce your Power Score to the allowed maximum for your level. Thank you!
Like that, the player won’t have to start from scratch, but he can modify a bit to fall under the maximum.
If they want to start from scratch, they can do that easily by themselves.
I will go and restructure mine to fall under the maximum.
Did you guys fixed the shield when the enemy’s offense is entirely made from ballistas and it’s upgrades?