Just listing a few projects built on it should really suffice to make the point. The Sims 3 was built using Mono and launched in 2009, Second Life went live with it in early 2008, Unity swapped to it after their initial 'front end' language began, in their words, "proving to be too slow and unwieldy." Their original language, quite appropriate for this topic, was Python! There's really an infinite room for discussion about this, but I think it's all a subset of the 'The Mono Question.' For instance your issue on exactly what open source license is used is completely redundant given Mono.
As for your divergence on 4 years not being a long time. I personally do agree. But our agreement stands in contradiction to the standards of software today. Entire languages are born and die in this span, libraries that didn't exist become ubiquitous, and in general 4 years is certainly far longer than necessary to expect some reasonable evolution of adaptation and opinion. The fact it has not is a peculiarity I find bemusing, and fun to consider. If nothing else, it leads to enjoyable discussion - which I suppose is the ultimate point of these forums.