Please keep in mind that the pixbuf loader for SVG is developed by librsvg and not the gdk-pixbuf project. This is the reason why it looks odd compared to other pixbuf loaders.
librsvg is written in Rust. This is what happens when you introduce Rust into a C project. The binary generated by Rust tends to boom in size. This is normal. I don't think librsvg as linked statically into the loader as you have guessed.