Exempting PD from the rout calculations would probably help, but my guess is it would be difficult to implement.
I have to confess, I normally play nations where PD is either strong enough, that having it die isn't a real problem, or else so bad, that you would never recruit any for any reason
So while I understand this argument, it doesn't have much visceral impact.
Maybe including rout behavior into the unit definition would be best. Unfortunately, there are 1000-some units, and they'd all need to be modified, since theoretically any unit can become a commander.
No es bueno.