I think TBN probably -should- be encouraged on auto-attacks. The nature of the shield is such that it becomes more effective inversely with the strength of the incoming damage (up until the point where it fails to break), and so that's actually one of its strongest points, except for having a duration shorter than the maximum time between two auto attacks.

If anything, TBN's biggest failure is that it's actually not as strong as it should be against the big hits and tankbusters, usually forcing the use of a secondary cooldown to safely survive (DRK's 3.x toolkit of Foresight, Dark Dance, and Reprisal would actually be tremendously useful in that regard).