what this "small business" rhetoric actually does is undermine unionization, and take away the bargaining power of workers. if the company you work for only has a handful of employees, you are at the absolute mercy of your boss - you cannot push back on anything. the result is a more stratified, class-oriented society with a larger bourgeois class and a subsequent underclass with almost no functional rights.
"small businesses" is code for "class war". it's divide and conquer.
leftists should not be buying into liberal rhetoric about small businesses; they should be pushing for big unions, instead.
in the context of an amazon, what that means is that what sanders is doing - pushing for the rights of the workers - is the better option. if warren has her way, they all end up as unpaid interns in unsuccessful businesses that are unnecessarily competing in saturated markets and that need yearly tax breaks to put off their inevitable collapse.