42093 C Model: Race Truck

[Philippe Hurbain]

I did learn a bit about part editing while using PartDesigner, but I get the feeling it’s not optimized for complex parts like these.

Definitely no. It's great to add patterns or connectivity on existing shapes, or to build simple boxy brick shapes. But to make complex parts, the tool of choice is LDPartEditor! https://github.com/nilsschmidt1337/ldparteditor
...BTW, nice C-model!