I with you now... I will try to answer your question the best I can... Fritzing generates .svg files in a number of places; when making a new part from an existing part, loading a new image into the parts editor, creating a generic header/connector, etc. I don't use Ink, I use CorelDraw which have different name for combining elements (weld, trim, intersect,..).
SVGs are a very complex format and there is no one standard. Every graphics editor has their own standard format. When Fritzing started, most of the parts were created with Adobe Illustrator (AI). Parts were created by different vendors... mostly by SparkFun with AI. AI was the standard at the time, Now because InkScape is free, this is the recommended graphics editor.
When Fritzing started they had to overcome the challenge on how to intrepid the idiosyncrasies of the different SVG formats. AI, Inkscape, and CorelDraw are all different and they all can be formatted in different increments (Inches, mm, pixels...), then when an element (rectangle, circle, text...) is rotated or altered, a new attribute is added (transform) which gives instructions on how to alter it. Fritzing did a very good job over the years to translate the various complex SVG formats into a simple format it could understand and use to generate its own SVG format...
I run into this problem all the time; some SVG files "path elements" from AI or Ink will explode or crash when imported into CorelDraw. Ink has the same problem when importing a CorelDraw SVG file. I sometime get around it by importing the .svg into Ink and saving it as a .ps file, then import into CorelDraw. I preserve the image but loose some data... like ID"name" (connector##pin)... but then add it back in and restructure the layers for Fritzing.
EDIT: The copper fill is generated by scanning the PCB one line at a time... The path that it generates may contain hundreds of nodes due to this scan process...