While I agree that they’re not being overpaid, 10% is a rather large drop in the bucket. Do they need that many to run an organization of 50 people, though? Perhaps they do, I don’t claim to know.
As a historical comparison, before selling out to Facebook, Whatsapp had 35 engineers, providing service to 450 million users. But perhaps they were selling their data at that point already, making this a bad comparison.