> Being snarky and name calling against site guidelines.
Ha, OK.
> Has this always been the case with Java? With C? With C++?
Its funny to see all the logical fallacies being used to try and counter a perfectly valid argument! What does this have to do with Java, C or C++? But since you asked, there were always open source compilers for C and C++ (GCC and G++ for example). Java - I don't know, I suspect not, but is Java popular with startups anyway? Why mention it?
> It has been open standard since 2001 and the current compiler open source since 2014.
Not sure exactly what Open standard entails?
Essentially, the original argument said that the software ecosystem for .NET has mostly been non-free and non-opensource until very recently (2014 - 2016 as you mentioned), which has meant that for at least a decade startups have avoided it in favour of open source frameworks, so even though it is NOW open source, the damage has already been done. None of these counter-examples actually contradict that original statement. By 2016 open source frameworks like Django, Rails, Symfony had been around for more than a decade and were no longer the "shiny new toy" but generally accepted as mature, stable frameworks on which to build applications. So I think its fair to say that Microsoft's approach to open source has been too little and far far too late.