OK, cash is unavoidable. But you don't tip taxi drivers in HK (beyond them normally rounding the change down to the nearest HK$). Bogus fees and routes are pretty rare from the airport ranks to major hotels. The approximate prices are published so they can't really mess you around.

From what I've read I guess there are as many problems with Uber as with taxis. With the added disincentive that it is illegal in HK, so there's a risk of being arrested, which would rather ruin your trip.