Mono and rainbow teams are shit at this point. Don't worry about it. Just summon when there's a good rate up event and fill your box with whatever you get. Eventually you'll end up with some good shit. I know, as I have a F2P JP account which started out fucking terrible (first 20-30 summons were all garbage), but now I've got Maxwell, Rosetta, Feeva, Taser, Alpha, Selena, Darvanshel, etc. It just takes time. But yeah, really everything is either OTK teams or a variation using a mitigator to survive.
Lunaris at this point is pretty dog shit. She was good maybe back in early Fall.
Also, don't get too used to the current BB fill rate. Lots of units are bugged, the worst of which being Elza. She's currently got 90 drop checks on her SBB, which is...uh, not even remotely close to correct.
My advice is to work on finding a healer (Lignes/Ulkina if possible), mitigator (Shera/Darvanshel/Narza pref), and infinite STBB'er (Arus/Rowgen/Lilith/Sergio). Max them all out, plus your Lilly and best Elza (either breaker or anima if you have). A good crit buffer is nice as well. Then, go and get yourself Karl and Grah. Max out Grahdens, then take down Maxwell. Depending on what units you end up with, you can do some GGC's prior to Maxwell to make it easier. But really with the current units it's cake.
Once you have Maxwell, Elza, a crit buffer, mitigator and healer, you can do pretty much the rest of the remaining content. Hope for a 2nd healer/mitigator for when raids come out.
Just for reference, my team has been Maxwell (lead), Orna, Lucca, Elza, Zelnite for the last several months. Maxwell is a staple (even still on JP, although I use Rosetta), Orna for crit/fire/thunder, Lucca for attack/earth/water, Elza for sparks, and Zelnite for BC/HC. For harder content (which there isn't much that I can't OTK), I'll throw Shera in over Lucca. Harder than that? Ulkina for either Elza or Orna.