I would highly recommend you check out my extreme mission guide, it has a lot of endgame tactics for hard missions and a lot of different teams that may work. I am level 100 and am finding the team below to work perfectly, I pop serial’s shields at the start of the mission and Mariana kills the rest.
Guide link:
Similar to the Gunderdome there is a trick to the start of the mission to avoid being instantly killed, see this video here:
But in case you are wondering how it works then see this video here of me beating the Stratus-Sphere with an example team and using this trick:
If you don’t have Ruby heroes then try using Kurtz execute technique, in this video Kurtz dominated but you can use flatline to revive if he cannot execute an enemy.