If microsoft, tomorrow, pulled the plug on the pylance LSP and removed all access, and the only thing left is the opensource version, the world is still at a better position than if they hadn't invested any money or opensourced anything.
This is strictly different from google owning chrome, because with that ownership, they have the ability to dictate protocols for the web.
The LSP is a protocol, which now is quite widespread, and will continue to survive and be enhanced, regardless of microsoft's involvement or not. The fact that they can choose to make some language servers close-sourced sucks, but being able to access a closed source component is _still_ strictly better than having zero access in the first place.