I think you're thinking too much in sort of "playground politics" and not about capitalist systems. It doesn't matter who is afraid of who, or who the big mean kid is. Microsoft dominates the charts in the Amazon software bestsellers: google doesn't have anything in that list. What does that tell you? You're comparing apples and oranges. The "IT industry" is no longer a single industry, so it's no longer about getting a bigger slice of a single cake.
When Microsoft does a major product launch that bombs (in the sense of Battleship Earth), then I'll take this proposition seriously. While they have chart topper after chart topper, there isn's a case.
I can see that your response to the "well they sell lots of software" argument is dismissive, but the fact that they do says a lot. It speaks to: market dominance due to historical monopoly; continued product development and support; and continued acceptance of Microsoft products by the marketplace.
This might sound simplistic, but these are the hard, cold facts. It's fun to predict the demise of a giant (and exciting and controversial). It's boring to predict that they'll lumber on, giant-like, for years to come. That's not interesting or newsworthy!
But sometimes the boring predictions are the most likely ones to occur.