By that logic people are using we could call pretty much anything a defender. I mean is a wizard who uses a lot of walls a defender, too? I think people are stuck on the idea that front line fighter=defender but that's only going to lead to a dull situation where each role is dominated by variations on the same archetypes.
It's more complicated than that. Controllers and Strikers are designed to be squishy. A glass-jawed Barbarian would go against archtype. Unless you want to make him a tough-as-nails aoe damage machine, which would be overpowered.
I like the idea of making the Barbarian a great crowd-control class, but functionally a guy who jumps into a pile of goblins and knocks them all flying still seems closer to fighter than a wizard, in terms of role.
A 'hands on' controller is a cool idea and a good alternative take on the niche.
It's an interesting idea, but that doesn't make Barbarian the best class for the job.