I've run the Fleet Excel R successfully as an all cannon build. I am a tac captain as well and though I presently fly a mobius, like yourself, I always preferred Cruisers to most escorts. That being said, there is no reason why you cant put together a successful build that, although wont give as much DPS perhaps as an escort, will nevertheless hold your own in both STF Elites (including defending the time gate alone) and or even PVP if you build properly both your ship and skill tree.
In the search section type in Excelsior Build (or similar). Tons of threads on how to go about doing this. Good luck.
"The world ain't all sunshine and rainbows. It's a very mean and nasty place and I don't care how tough you are it will beat you to your knees and keep you there permanently if you let it. You, me, or nobody is gonna hit as hard as life. But it ain't about how hard ya hit. It's about how hard you can get hit and keep moving forward." - Rocky Balboa (2006)