Hello Ahnfe,
such object can be tricky. It looks like it is all white, so it can be without important features for better alignment. It looks like there are some misalignemnts (according to the mesh result) Probably you will need to create some noise over the object (like by using the data projector, to get better mesh. Like there, but with other feature source: Tutorial: Using Scanning Spray to Scan Shiny Objects ). .
As you used also mobile, have you kept the camera priors active for such images?
Also, I woudl say that 600 images for such object is not enough. Also, the capturing path seems to be insufficient for me. You should cover the whole statue following the shape of it. As I can see on your screenshots the coverage is not so regular.
Also, have you provided the simplification to 3M tris directly from High resolution mesh?