Nope, it saves me (a) keystrokes and (b) design effort. The restricted subset of color options, for example, lets me use a predictable color system out of the box without having to think about it. It's not about removing "complexity" in the sense of understanding how CSS works.
With a stylesheet you have the styles in one place, with Tailwind you repeat it on every element. Yes components and copy/paste are a thing but I'd be very surprised if you're having to manage less style code with Tailwind. As for design effort, setup a few primary/secondary accent colors as global variables.
Not exactly - with Tailwind you aren't repeating the design decision, only the scalar value. So `border-2` might mean a border width of 4px or 6px or whatever, but that's the design decision that is encapsulated within the theme configuration.