I agree Uber is employing a ton of dark patterns and their fees are absurd, but for tips at least I think this is appropriate and ethical and is how I tip in person if I have a coupon or something. Tipping is about compensating workers for the value of their labor when their base compensation doesn’t appropriately do that, as it generally doesn’t for restaurant workers in the US. If you get a sandwich for half off or whatever, the cook & the delivery person still had the same amount of work to do, and the tip should reflect that.