Falk:
I've managed Dark-weak with no AASB, but that's mainly because I had non to use. Put Dark God Cloud to good use there, backed up by Seifer chain + Radiant. It was 11 hours of hell though.
What was your lightning-weak one? I'm struggling with Bartz and Rydia AASBs - no en-lightning means their damage tanks in Phase 3, especially Rydia who becomes useless. Tried staggering AASBs but it hasn't worked out. And my other lightning DPS is either too hone intensive to last to the end (King USB/Shantotto USB), time restricted (Sora USB/AOSB), or laughable (Ashe Glint/BSSB).
re: Elemental Proving Grounds
Managed to get up to 3,148,446 by changing Bartz' RM to Gathering Storm (he was running Wind DMG+ before) and putting back him LMR1 (he was still running his LM1 for Titan). Tweaked a few more turn orders, went with RW Tactician's Tome, and managed to squeeze out 3,319,171. And that was with no real multi-casts from Bartz, so I could do better, but it would be too RNG for my tastes. I'm good with this.
Full team, for the record:
Ignis (LMR): Wrath, Entrust, Acestriker (BSSB)
Cloud (En-Wind/DC-Wind LMR): Raging Quadstrke, Scholar's Boon (Glint+/USB1/AASB/AOSB)
Faris (DC LMR+LM2): Storm Assault, Wrath, DMT (CSB/SSB)
Bartz (LM2+LMR1): SSS, Gathering Storm (AASB/AOSB)
Elarra (LM1+LM2): Crushing Tango, MM (USB1/USB2)
Rough turn order:
Ignis: BSSB, CMD2 Bartz, Wrath, Entrust Cloud, Entrust Elarra, whatever
Cloud: Glint+, AASB, Raging Quad, USB1, Raging Quad x2, AOSB
Faris: CSB, SSB, Syldra, Storm Assault, SSB1, Storm Assault if possible
Bartz: AASB, SSS spam, AOSB
Elarra: USB1 after Cloud Glint+, USB2, RW, Crushing Tango, USB1
Cloud doesn't get USB1 up until under 8 seconds left on the timer. But at least he's under HQC at all times. And at least for his last two RQs, Cloud gets to hit 45000x4 and then 56000x4 each.
On the 3.3 million run I managed to squeeze out both AOSBs with 1.00 left on the timer. Bartz capped, Cloud hit for 30,000x20+99999. Also snuck in one last Store Assault from Faris for 5500x4. Nice.