I'm clearing just fine with my Water team (though I haven't run up against Thunder recently). You're running with a bunch of SRs and don't even have Cthulhu, so some trouble is to be expected, especially if you get thrown up against Thunder all the time. Like I told you last time, Mordred's debuff is very important for consistency if you don't have elemental advantage or elemental resistance down. Also, the way I think of it, I'm running Sundays for the chance of Water SRs/SSRs. If the 3rd stage is Thunder, I don't need to clear it. I just need to clear the 2 stages before that to check the element.
I cleared it without deaths on that very first Sunday (Thunder on wave 1 also). You must be running without Black Propaganda, which isn't advisable. With only -50% ATK, I might be able to kill him before he uses the 2nd Overdrive on turn 9 (should be possible since the first Overdrive will speed up the 2nd Burst). If not, bringing Snow Raphael would delay that to turn 12. That's definitely enough time to kill it. Alternatively, running SSR Nike and Shiva instead of Sol and Gabriel might boost DPS enough to clear by turn 9. Gaia might also be a better choice than Sol for Accessory Quests with ATK capped at -50%.Thunder wave2. I've had lots of wave1 and wave3 Thunder before, but not this guy. Is he even fucking POSSIBLE to beat with Water? This little fucker hits everyone for 4k every 3 turns with -50% Atk. I think I could've handled him with -70% Atk, but in two weeks, that's not a thing anymore.