> Is most of the work on the schematics therefore done through this, or manipulating the binaries themselves? Why Altium and not text based kicad for this? I presume just for the ‘professional features’ Altium has

I'm just manipulating the file format directly because I don't want to be tied to Windows (bleh). I only fire up Altium for a few features that I haven't implemented yet like the autorouting and the UI automation was to let the LLM figure out file corruption issues.

I learned Altium long before KiCad was a viable option and Altium's ActiveRoute routing is the perfect blend between manual routing and autorouting so it's really hard to switch. ActiveRoute gets even better with the LLM filling out all the design rules.