LOL, most of the brutes I see on team really don't care if they are outdamaging a tanker or not, if one is on the team. They just go in and "H<redacted for copyright>K SMASH!"
I think folks are too obsessed about who does more damage or doesn't.
Are things dieing? Brute and the Fury mechanic is doing its job (or any damage at really)
Are things being pulled at the tank so that squishes on the team don't die? Tank and Taunt, etc is doing it's job.
EDIT: I don't think giving tanks a little more damage is going send most brutes into the corner worrying about working harder. They will joust go about their business.