As we know the lances are 1-shot abilities that hit you with 100% accuracy anywhere up to 15km away from the unimatrix. It's broken, yeah, and there doesn't seem to be much interest in fixing it. So if you are going to play the mission you are just gonna have to deal with it.
Best way my fleetmates and I have figured out to beat this segment of the mission is with spam and sci abilities. The AI doesn't seem to differentiate between players and pets/mines... so use that to your advantage. Have mines and pets flying around, gives the unimatrix something besides the player ships to target with lances. If there are 5 targetable things on the map (players) then you've got a 20% chance to get popped. If there are 20 targetable things on the map, well, you get the idea.
Having a drain build on the team is also a big help... enough drain can actually shut the unimatrixes down for short periods of time. With plasmonic leech, tykens rift, energy syphon and subsystem targeting you can really put a damper on the Borg in general. Klingons gain an added bonus with aceton assimilator and energy syphon carrier pets.