Just out of curiosity, how did you decide that Daka was the weak link on that squad? I would personally guess that Vader is less useful at those Star and Gear levels. A quick glance and I would guess you need more burst damage to climb easier.
B2 is always a great choice, can be plugged into any team, and will help against those pesky rebel buffs... but doesn't help at all with damage. 88 would also be a good addition, as noted above, and would give you the damage boost I suggest.
I might also recommend going ahead and leveling up your Geo Soldier, but perhaps grab Geo Spy in addition (highly underrated and will fit into that dark team, if you're trying to stay dark). Geo Soldier is extremely easy to level and gear, and I like him a lot for this reason.
On a long-term outlook, how is your scoundrel squad? Once you get beyond level 70, you reaaaally want to be able to complete the highest tier of the credit heist event. It's the only way to efficiently level your roster at higher levels. For this reason, 88 and STH could be better long term use of your crystals and energy.
