Been a Thunder main since I started just because of RNG, perhaps I can give some insight.

Raiko speeds up your team burst and helps you survive AoE attacks
Athena is queen against water but is still useful against any boss with extreme dmg to single targets. IE those deal 12k 3 times attacks

Mammon, Baal(u), and Updated/Awakened Tyr all perform the same function of being a core damage dealer.
Mammon pros: AoE def down, Curse Desires hitting for 700k is nice.
Baal(u) pros: AoE resist down, quite fast with double/triple proc often
Tyr pros: With the rework she can now choose when to increase dmg, doing so on burst, hitting 2M burst without Shingen is nice.

The only other SSR Thunder I have is Justitia. Her gimmick of taunting/ulting/fort/taunt/ult/fort for 5 turns while sitting at 1 health is amusing ... but not as practical as other hime.

I tried for Thunder Aphro but had no such luck during the holiday events, ahhh well.