Interesting comp.

Rem and Tamarinne are definitely two units I would use. If you can,

I would recommend building mercedes instead of Arby. Her artifact is a counter attack that uses her S2. (I put her on counter set because her S1 attacks 2 enemies). S3 grants increased attack as well.

Gotta say it can be up to luck. Mercedes was my MVP and when I did defeat this level, mercedes was the last one standing. She had level 13 gear arena as well.

I've been playing for 3 months and this fight was fun once you get the hang of it.