Please stop repeating this incorrect corporate structure. While there are still 3 entities, they are all now owned by the same German holding corporation, L&O Holdings, which is owned by 2 German individuals. The holding company now includes Sig Sauer USA, Sig Sauer AG (Swiss), and Sig Germany.
I do agree with your assessment of quality between the companies, though.
It's unclear to me how much L&O Holdings actually does to bring the two remaining Sigs together (Sig Germany is defunct as of 2020). They do not sell each others products, do development cooperatively, produce cooperatively, etc as far as I've seen. Sig Switzerland issued that foot-in-mouth memo backing the P320, so there's clearly something happening between the two, but I think presenting them as separate is more accurate than claiming they have a close relationship because the same holdco owns them both.
That's not correct. Sig Sauer USA's VP of Engineering Adrian Thomele was originally an Sig Sauer AG employee, who owned a company that was acquired by Sig Sauer AG. There are other examples of engineering management propagating from the German/Swiss entities and sharing IP between one another. Secondly, Sig Swiss AG recently announced that they would be manufacturing the P320. The German entity was shuddered to decrease manufacturing costs and effectively offshore to Sig Sauer USA, who is now also offshoring more manufacturing operations to India. I think there is much less independence than you might think between the entities.
Some more history you might find interesting - Thomele & Mayerl designed the FCU and P250 that would ultimately be the foundation for the P320. Thomele then went onto some of the design work for the P365 from my understanding while the P320 was going through trials and having issues. He's been in numerous depositions along with some of the US engineers that report to Thomele now like Sean Toner.
I do agree with your assessment of quality between the companies, though.