The difference in effort delivering 2 vs 10 items isn’t anything close to linear with their cost. I would suggest a fixed minimum + low percentage of the total order is vastly more reasonable than assuming you need to tip some silly multiple of the total bill. But even butter is to simply avoiding all businesses that use tipping, it’s both less mental effort and generally cheaper.
Is it really? Genuine question! I'm from the UK, and here a tip is generally seen as something which is given for exceptional service, rather than subsidising an employer's lack of remuneration for the job at hand.
So my personal approach to tipping in the US is that it starts at a base level as appropriate compensation, and goes up from there for quality of service (or very rarely goes down if service is atrocious).
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.