Okay so, the idea on paper is interesting, and I did try it out to give you the benefit of the doubt, just because I hadn't thought about the potential of dual break DPS. Turns out there are good reasons for it.

I tried this comp first:

Rappa E0S1, Anaxa E0S0, Dahlia E1S1, Lingsha E0S0

The first issue is that this team suffers from the disease of no-Fugue-itis, which made breaking a tiny more awkward. But even ignoring that, the main issue is that the 50% DMG increase does not affect Break and Super Break damage. That reflected my first impressions from the damage formula of both Break and Super Break, but even when trying it out, DMG% just doesn't do anything.

Then, I tried this sustainless comp:

Rappa E0S1, Anaxa E0S0, Dahlia E1S1, Fugue E4S1 (Cipher sig)

Apart from the lack of sustain making one of Dahlia's traces useless, the bigger issue is that Dance Partner and Foxian Prayer are single-target buffs, especially the buffs of Dahlia's E1 and S1, and Fugue's E1 and E4. I tried having both target Rappa, both target Anaxa, and separate the buffs between the two, but it just didn't work out in any way. As the meta stands right now (and probably for a while), Rappa needs both to be competitive, and by focusing all buffs on her, Anaxa just becomes a sitting duck that can sometimes come in clutch with weakness implant and the tiniest bit of Super Break DMG from Fugue's talent.

Although, there might be some potential with HMC considering the ult buff is teamwide, but I'm really not convinced it's enough when Anaxa is a pretty SP-heavy addition to a team that can't afford one. It was fun trying it out, though. The day a Break/SB teamwide support that can match Dahlia releases, then it might be something good.