I agree that mobile and search were missteps, specifically putting themselves into a position of competing so poorly in those areas overall. It's also unrealistic to think that one company could own desktop, mobile, search, office, etc.

Microsoft was going to own desktop, mobile, search? $300-$400 billion in revenue? $130+ billion in profit?

No. That's absurd. Holding Ballmer to account for not conquering planet Earth is not a fair premise. Of course there were lots of 'missteps,' what's described is impossible. Their biggest mistake was attempting all of it in the first place.