per project you can decide what those sizes are and everything just falls into place… you rarely really care what the size is in pixels; mostly you only care about sizes relative to other parts of the UI… so again, people joining on a project don’t need to memorise magic numbers, because they just know without needing to guess what the size suffixes are
You can do all that with a CSS variable though...
I think the text- and font- prefixes are emblematic though; because you end up with this soup of classes on every single element, they have to be as short as possible, and so they can't use font-size and font-weight.
I can imagine it working nicely for flexbox, because that is complicated, but I still suspect you're better off just using the effort you would need to learn the tailwind classes to instead learn plain flexbox.