It sounds simple to me but is probably harder to implement.
Make AC matter. Get rid of the ac bonus to tempest and force people to either go heavy dps, light on AC or vice versa.
or
Allow a shield block to deflect a significantly higher amount of damage so that actively shield blocking becomes a skill set wanted in groups.
I have both a twf barbarian and a f/p/r S&B. I like playing both and I'd probably play the latter more if you didn't have to get intimidate to an absurd level to be effective as a "tank".