From reading Reddit apparently double Avante is strong enough to justify farming middle post nerf, might be true for double zedus. I've got no zedus, griff, Dion, or Diana.
Wow.
Of those last units you listed, the only one I'm using myself atm is Diana, but it sounds like she is more of a substitute for Shida who is actually superior for it. I'd definitely need a Zedus/Avant type to even attempt Middle farming after the nerf though.
The group I scored 18.1M with was:
Kira (Lead - not doing a whole lot for me other than being a crit leader though, no longer a light/dark team) - Crit buffer
Quaid (I wish I were Shida) - Elemental Retyper
Ultor (Call me "Beastmode") - Massive ATK buff, +Crit Damage buff
Diana (Utility MVP) - non-Attaking SBB with BB fill to help along the whole Overdrive situation for UBB's
Gazia (Nevermind being a mitigator, this guy is an offensive beast under the right circumstances) +ATK conversion buff +BB% buff
Zedus (Friend Lead) +Crit +Spark +Everything else up to and including Foul Language (+200% Foul Language buff)
Kira's elemental weakness buff is only helping himself and Gazia there, and even then only vs the occasional 1 Dark mob on the screen (I still don't care for Dion) - Reis might actually be a better option for me just by virtue of the fact that he personally whips more ass. I lack a secondary spark buffer that would beef up my score a lot on UBB rounds, but I hesitate to try to work Zenia in because she clashes so hard with Gazia on his monster +300% BB buff which is no joke. Would losing 100% BB damage be worth an extra spark buff? Yea, probably, but still.
She'd be dead weight on non-UBB rounds and maybe a liability, but she does do great personal damage.
The Zedus friend just by himself brings so much to the group it is scary. I can only imagine being able to layer his UBB and SBB's on the group at the same time.