To me all his assumptions seem pretty reasonable. Since Uber isn't providing a detailed breakdown, all we can do is estimate. And if we're willing to accept the basic assumption that people respond to economic incentives, remember that Uber's incentivized to be as misleading as possible in their favour. Even if it turns out they're completely lying, there's a reasonable chance that the economic benefits from building network by doing so are significantly greater than potential future costs if someone found out they'd lied. Given that context, I think the author was actually being
overly generous and deferent to Uber's stated numbers.
My father-in-law's an NYC taxi driver, and before that (in the 90s) worked for a black car service. So I can tell you from inside experience that you make more money in Manhattan than anywhere else, period. The fact that Uber drivers have the freedom to go to New Jersey or Far Rockaway or wherever doesn't mean that they actually get any benefit from doing so.