Twin strike is now exactly what I wanted it to be: a tool to mark two opponents, rather than a damage boost. Perfect. Looks like I may actually play a tempest fighter at some point now.
Not only might I play a tempest fighter at some point, or a battlerager vigor fighter, I won't feel like I'm gimping myself by playing a different defender. Both builds were so much better than other classes and other fighter builds I felt if I made a defender to add to my party I'd be a 5th wheel, trying to compete with the battlerager vigor fighter in terms of defending or damage dealing. I felt like, since our battlerager vigor fighter was so invincible and did so much single target damage, that I didn't need to build a defender for the group. The problem, however, is that the fighter is the guy who is most likely to miss a session, and we don't like to have to play his character when he's not there. So I kinda wanted to play a defender for sessions he misses.