> I personally would get panic attacks and couldn't sleep anymore if my dependencies aren't open source and I would depend on a company for any reason. But that's just me, it definitely sounds very mature
.NET is open source.
To my understanding the "batteries" as in "batteries included" from above aren't.
That includes also all the "batteries" (https://github.com/dotnet).
I dislike nodejs for the same reasons. But do get the feeling that rust and go, maybe even something more exotic like elixir would be good alternatives as well for your use case.
I have barely anything to compare to your requirements tho. I personally would get panic attacks and couldn't sleep anymore if my dependencies aren't open source and I would depend on a company for any reason. But that's just me, it definitely sounds very mature