My sith trooper is nodded completely for defense and tenacity.
It just requires knowledge of kits and building on strengths. So in k2's case, modding for tenacity is fine since you sacrifice 0 protection to get it. There are no protection sets and tenacity primaries only share cross mods so he can still get a prot circle, triangle and arrow. All while building tenacity sets.
Not counting secondaries, k2 can get upwards of +54% tenacity and +90.5% protection. He doesn't need to hit hard, he just needs to be able to counter and regen prot.