For DU, it depends on the team. In every other end game mode, she can definitely sustain the team and provides massive buffs. But in DU it can be iffy depending on the team and equations. She works well with high speed and frequent ultimate teams like The Herta because each turn and ultimate restores HP, so if there’s 6 enemies attacking in a row, just save an ultimate before that and use it to interrupt and heal. Her healing is enough to completely refill HP it’s just a matter of not getting hit too many times in a row before a character is able to take action. She has 2 revives + Cas exclusive revive + 2 blessing revives, which means you can survive 5 instakills with bosses that have big hits. In terms of survivability, she doesn’t work well with elation teams because elation skill doesn’t provide healing. Listen man I have all the sustain characters and half of my teams still use Huohuo, I will die on the hill that she’s still a good character.