I guess it is 1. If your competetive edge is running a slick taxi operation, having that many employees seems ... counterinuitive. That is probably why Uber gets a "what are they all doing" alot.
I mean how many corporate employees would you have if you ran Uber?
Uber on the other hand is an app together with some driver administration. The main operation of the taxis are on the drivers.
Then, on top of that, you've got 91 million monthly active users. Assume each one takes only one ride per month, and only 1% of them have some kind of issue that requires them to reach out to support - that's still 30,000 new issues per day many of which will require coordinating between both parties involved in the transaction.
Do they have more employees than they need? Define need. It's easy to hire above what's necessary to sustain operations when the cost of capital is cheap. More people can develop new products and grow margins for the business overall. But Uber is seriously far from "an app together with some driver administration" any more than Amazon is "a website with some seller administration."