Uber is global, your local tax company is not. Plus your local tax company is restrained by you know, laws.
Amazon vs Walmart is also not a good comparison .. I believe this david vs goliah is mostly start up people that think too highly of themselves! In reality you have Google, Facebook, Amazon, Apple, Microsoft... all huge companies that have been dominant for decade + and aren't too different from the post.
Walmart is actually doing very well, especially in e-commerce.
As it stands, you have the poorest Americans (the long tail) competing against a small section of the rise who can afford and trust that shipping goods to their door. The overlap is minor, excepting for perishables.
David is so far ahead Walmart is looking in the mirror thinking they're ahead :)
Amazon ate Walmart alive, alone with a handful of other retailers.
Etc.