Probably shouldn't have auto'd it. I just ran a rank3 with my thunder team and didn't have any problems with it on manual. I did lose 1 hime during the final stage because of the boss' raging overdrive 1shot one of my himes even with Raiko's damage reduction skill up and using double Yggdrasil, which was also my only source of heals. I might have been missing an atk down debuff, since I used it on the previous stage. As long as you save a full burst for its raging overdrive it's pretty easy. Its regular overdrive just increases its rage meter with no damage and she has a very long stun duration.
All final bosses seem to be the same for each element, which only differ between ranks.
Rank4 on the other hand, I am very reluctant to even try, I might later for the Dark and Light accessories when they up.
Seems the goal as of right now is to get the SSR accessories which have up to 3 effects that drop from rank4 quests (i think?), or you can grab the easier SSR rings which only have 2 effects from the shop and the clear. It seems these effects are randomized too.
A little worried this might burn through my break limit mats if I start running rank3 (and eventually 4) 3 times a day.