It's much more than that because it can make use of CSS pseudo selectors like hover, which is not possible with inline styles.

Under that definition any css class is a shorthand for inline styles

There's a big difference between utility classes which are shorthand for inline styles (random example from Tailwind's site where every single class is a one-to-one mapping with a single style override.):

    class="ml-3 hidden rounded-lg bg-gray-100 px-2 py-0.5 text-xs/6 font-semibold whitespace-nowrap text-gray-700 lg:block dark:bg-gray-400/15 dark:text-gray-300"

and semantic names which use the CSS cascade:

    class="main-content subheading"

Calling that a shorthand for inline styles is just being obtuse.

Media queries, pseudo selectors, extensible design system with sensible and practical defaults, and many more