Battle Rage doesn't come with the text "only usable by Patron Warrior". If there were ever the possibility that some other kind of Enrage/Self-Damage warrior were to emerge, which is an archetype that Blizzard has always tried to push (if not somewhat unsuccessfully), than nerfing Battle Rage would affect that deck as well. And as I said, that's a pretty significant hit to Warrior in arena.
Swapping the attack and health of Warsong Commander to a 3/2 only significantly hits any kind of enrage deck that can double whirlwind and generate additional more little dudes after the second whirlwind.procs. So that really only hurts Patron and... Dragon Egg.
Swapping Warsong's health and attack wouldn't do much because the Charge she gives minions is a permanent buff, it's not an aura effect (think Hobgoblin, not Stormwind Champion). Warsong can die in the flurry of Whirlwinds and your Patrons and Frothings will still have Charge, provided you played them before killing her.
I still think the best way to nerf the deck without killing it is to make Frothings a 2/3 or even a 3/2. That would put a cap on the amount of damage you can do in one turn but still leave the rest of the deck intact.