I like this idea. It is very simple, yet would solve the situation quite well.
I’m not sure if debuffs would have to be disabled. It would give you an advantage, but many leaders also have a nice combat bonus which you would forego, and it would solve the “my buffer heroes keep dying randomly” issue.
Maybe cut their buff in half? So you would be forced to pull them into danger for the knife-edge battles, but could still benefit from them otherwise.