That and I'd like to add:
What makes a superior frontman? It's the mixture of voice, selection of songs, verve and charisma.
You could argue that Brian Johnson is the better singer, although I'm undecided on that one. He brings more energy to the stage than Bon Scott, I give him that. Bon Scott had a far better ratio of all-time great songs that Johnson, I doubt that anyone will argue with that.
It's in the category of charisma though where this battle is decided without the shadow of a doubt. Bon Scott is among the top 10 most charismatic frontmen in rock history while Brian Johnson is just a curly dude dressed in a wifebeater wearing a stupid hat. Bon Scott oozes charisma, he's diabolical, creepy and looks like a stereotypical sexual predator.
Bon Scott easily wins this battle for the same reason why David Lee Roth beats what's his face.