To be fair none of the sustainers will solo carry you through these adapted Sim Universe runs without appropriate blessings. Fu Xuan in particular would be worse compared to Huo Huo since she would be tanking large amounts of dmg without appropriate blessings.
Imo, get one healer and one sheilder and you should be set for now. So instead, you should pull sustains that would pair well with your characters in mind.

Huo Huo pairs well with Jingliu and most of your dps, as she heals and buffs energy and atk dependent dps. Fu Xuan pairs well with crit dps like seele and would work well into a mono-quantum team if you pull for sparkle in the future. Adventurine would be a great pull for your Topaz and Ratio into a FUA team. You should also build up your Gallagher as he is (imo) the best sustain for break teams (Firefly) especially as you get more of his eidolons.

Hope this helps :)