Clara. Her debuff is Svarog's mark implant on enemies when she gets hit. E1 also makes this mark permanent if the enemies who hit Clara aren't dead. Still, Topaz is the better option for consistency and her talent buffing FuAs in general (not just Crit DMG like Robin). You'll feel the difference. Sry for the word vomit too lmao
The 4 star coming in 2.4 is actually a really good replacement in a team style like this, cause without topaz/a fua support this just becomes a ratio hypercarry team which is valid in its own right but yea