OK first of all I don't post these very often so I apologize if it comes off a bit gruff.
DPS does not matter in this mission... noone cares! Unless you are running a full out group of 5 tactical ships and have more DPS than the borg and can obliterate the enemy forces in 30 seconds or less it's not going to help you. (and I mean all of them)
Everyone does these missions for fleet marks. So lets try to maximize that.
First off let me say I've heard a lot of people using the excuse that "Zomg we have someone who isn't a vice admiral in our group in our group were doomed"! This is a load of hooey! I have succeeded in saving 18+ ships plenty of times with people who were not vice admirals. If all of them aren't then it might be a problem but otherwise... stow it.
Primarily you succeed at this event by "healing" the freighters not by how much DPS you do. Level doesn't really matter as long as you have some healing abilities on your ship and know how to use them.
Now I will be the first to admit DPS is a huge deal in the defend the Starbase misisions both fleet and groupbut again let me say "not in this mission".
First off some helpful abilities for you ship if you plan on doing this mission. Notice that all of these can be gotten at lower levels too and they can still be effective.
BOFF Abilities - That help Tons
Tractor Beam Repulsors - (Science) I cannot stress this one enough you can push the enemy ships away from the freighter. This helps reduce their concentrated enemy dps immensely.
Transfer Shield Strength - (Science) A shield heal and damage resistance buff. If can keep the freighters shields up they will not get demolished by enemy torpedoes.
Tactical Team - (Tactical) This is another one I cannot stress enough. Using Tactical Team on the freighters gets them to pour their shield power to the side/sides they are taking damage on. Handy for keeping their shields up on one side if you don't have a shield heal handy.
Extend Shields - (Engineering) Again a shield heal and damage resistance buff. Very handy for keeping the freighters shields up.
Eject Warp Plasma - (Engineering) A Dot + Slow Movement this is another good one for slowing down pursuit and allowing the freighter to make it safely to the station.
Fire at Will/Scatter Volley/Point Defense Turret Console - (Tactical [The console not as much]) These all server the same purpose killing fighter and torpedo spam which also keeps the freighters up longer.
Gravity Well - (Science) Another Excellent choice for holding back the enemy via CCing them into a ball and keeping them there while the freighter gets away.
Hazard Emitters - (Science) Hull heal over time if the freighter is getting tractor beamed or banged up by torpedo barrages.
Engineering Team - (Engineering) Instant Hull Heal for damage freighter just watch out it's on the same cool down as "Tactical Team".
Science Team - (Science) Shield Heal Instant. Not nearly as good as some of the other abilities IMO because it shares the cool down with Engineering Team and Tactical Team.
Anyway that's it for the abilities that I use on a regular basis. Even the couple of tactical ones in there aren't in there for dps purposes they are in there to help protect the freighters from fighters.
DOFF's - That help some too
Matter/Antimatter Specialist - (Space) Adds a percentage chance to "Immobilize" you enemy for a few seconds with eject warp plasma instead of just slowing the enemy.
Conn Officer - (Space) There are two the one I am talking about lowers the cool down on "tactical team" and buffs your starship maneuvers comes in handy when you only have room to slot 1 tactical team.
Maintenance Engineer - (Space) Reduces the recharge time on engineering team and buffs starship hull repair.
Developmental Lab Scientist - (Space) Reduces the recharge time on science team and buffs emitters.
Next - Rules of Engagement
1. Don't Bunch Up. What this means there should be no more than two people on any one freighter period. I regularly save freighters on all three of my admirals by myself with any of the three ship types. You are not helpless because you are Tactical or an Engineer.
2. Keep the Freighters Shields Up. If you keep their shields from dropping they won't take nearly as much damage making everyone's job easier.
3. Heal the Freighters. I don't know how often I have to say this in groups but it's too much. If you see the freighters hull getting low toss a heal on it!
4. If your freighter gets destroyed. MOVE ON don't keep engaging the enemy! You are going to be a lot more help to the rest of your team than avenging a blown up freighter that doesn't care anyway.
5. If you freighter finishes unloading it's cargo. MOVE ON there is no reason for you to engage that group of enemies at that point! You're better off helping the other groups.
Following these pieces of advice can be the difference between getting 17 or 18 marks from a mission and 40 to 50 Fleet Marks.
Personally I like 50 better. Hopefully this helps someone or a group's farming of marks easier I know I would like it to be.
Dr. Julian Bashir: Out of all the stories you told me, which ones were true and which ones weren't?
Elim Garak: My dear Doctor, they're all true.
Dr. Julian Bashir: Even the lies?
Elim Garak: Especially the lies.