I find it really difficult to work with someone else's code, so I wrote my exporter from scratch.

I did yeah

Problem: https://i.imgur.com/GjlBn7T.png
Solution: https://github.com/bonjorno7/SourceOps/blob/feature/armature-export/model_export/export_smd.py
Here's my smd exported that does export them correctly, pls take a look.
Especially at how I use bone matrices, should be all you need.
It's open source, we can help eachother :)