I think this is true for all Uber drivers, if they account for their explicit costs (gasoline, maintenance) and hidden costs (depreciation on the vehicle).
The "black car" drivers get a much higher rate, but unless they get regular bookings, it doesn't help. And, it may also depend on the area, and the policies.
For instance, I live on the fringe of a large metro area. Uber only matches a customer with drivers within about 10 minutes away, and regular Uber drivers are rarely within that distance. But, Uber will instead offer "black car" service that is 15-20 minutes away. The price is about double the "select" rate, and about 3 times the "regular" rate, so we don't use it. However, the "black car" driver also has to drive further to pick up a paying passenger and eat that cost.
If your friend cleared $300/day, that's roughly $75k/yr. Work 5 days a week, 50 weeks (weekends off, 2 wk vacation). I don't think they are making that much.
He doesn't make $300 every day. But even if he did, that's $75K gross. It doesn't account for his cost of maintenance and depreciation.
Manhattan is almost all “black car” level. No ride sharing level or whatever they call it. Your observation matches what I have been told: with the shorter fares, drivers may actually lose money after expenses.