Several problems got in the way, however they are related to the previously mentioned ones.
First, it was all procedural
-filtering generated the shape's distortion, the 3D shading, the bumps, the defocus at the sides and the 4 colour painted texture, as well as the drop shadow. Atop of that was an overlay effect filter and a filtered background image below.
What didn't work:
the blend filter primitives blending the object into the background image, and
generating the overall shading by blurring only.
Had to remove those -the overlay effect was added in "post production", applied on a raster image to gain rendering speed. The dropshadow is a simple radial gradient instead of a blurred object in multiply mode.
And, the 3D shading is now the result of many flat filled paths on top of eachother, and the filter uses the object's luminance. Here the compositing could be tweaked a bit more, yet this one got way out of hand.
Better redrawn it from scratch next time.