The defense for MS that I see a lot is that Bill Gates is a smart guy.
I agree with everything you said.  MS is ruthless.  Bill Gates is ruthless.
But let me be very clear.  I don't offer Bill's intelligence as a defense.  There is a tendency when people are against somebody or something to think that somehow any claim that anybody cares to make against the person or thing is true.  There's a lot of people who say BG is stupid or Microsoft is stupid.  That's just not true.  There are a lot of smart people working for MS (unfortunately, too many of them are lawyers) and Bill Gates is among them.
Also, there are a lot of reasons why MS is dominant, and ruthless, shady business practices are only part of it.
k