Just because someone is a professional online ranter it doesn't mean they are always right.
I have a basic understanding of what dropbox is. I've never used it. Never even been to their website. I don't care about synchronizing files. I suspect I'm not in the minority.
There was even a "college space race" to get more storage a while back, https://www.dropbox.com/spacerace
100 million account (including me)
4 million paying customers.
Which means, almost none of MS's customers.