I used to have this same problem with my Tatical officer. However, I have started a new character that is an engineer and having the ability to recharge your own shields makes a world of difference. My away team is made up of one addition engineer, one tactical, and two science medics. I'm using a sniper rifle, so my strategy is usually to have my away team attack the boss, then hit him with one super shot, then start sprinting around so he cant melee me, while continuing to recharge my shields and attack him. After he's down move on to the next most powerful and repeat.
OK. It seems, so far anyway, that the problems were all in Delta Volanis. I have had just find ground combat elsewhere. I'm be sure to ticket which systems are spawning undefeatable klingons.
Thanks all for the advice and reassurance. :s
See my post above. The "problem" is not confined to just one Nebula, nor are the Klingons "unbeatable". You can in fact beat them with the right setup. It might not be on the first or even the second try, but it is possible.
As a Science Captain, the method I have found best for me is to freeze the boss character and keep him locked down while my team takes out all other combatants one by one. Then, I have hyposprays at the ready and we all gang up on the others. The order which I usually work is healers (highest to lowest rank), science officers, shield-less trash, then lowest to highest rank on everything else - all the while keeping the highest ranked non-medic enemy locked down.
It takes a little used to to juggle between freezing the big bad and assisting my team, but it works well. Just remember - 'Y' is your best friend in ground combat.