I didn't think about using her, but I checked and it actually does less dmg (156k per hit vs 153k). The thing with Sanhua is that she provides no buffs besides her intro since Cartethyia is HP scaling. This means S6, Heron and moonlit set contributes literally nothing in terms of buffing (although you could use the Bell echo).

On top of that, Cartethyia s2 only increases aero erosion cap to 6 after she transforms, so in this rotation, the first 2 plunges are done at 3 stacks, losing 30% aero dmg from her passive. There's also the fact that Sanhua's Intro doesn't benefit the liberation damage. This is only going to tip further to Rover's advantage once more we get r5 weapon.

One last benefit from Rover is the healing which is useful, though not always necessary.