Returning player question

Hey all, didn’t play for a couple of years. 80% of my gameplay time are rated arenas. The question is about super bunker core Necromancer/ tempest builds.

I just don’t understand, why they have soooo much sustain.

Is it possible to take them down solo? What should I do if I play power mirage mostly.

Condi mirage is viable now? Tested couple of games, and it seems like there is too much condi cleanse in group battles, and I’m useless.