Yes, MSFT acquiring GitHub was like if the Pope, supreme pontiff of the Catholic Church has announced that they are taking control over CERN and promised it would remain an independent research organization.

What choice would all the scientists have in that case? They can't just say: "I'm leaving physics until someone else builds another LHC".

Until we have a better, more superior, free, open-source, public service that can do things better than GitHub, I'm afraid we'd have to play along.

But the point is not about GitHub vs. something else. It is about that Pull-Requests are preferred over mailing lists for open-source projects.