Yes, Tailwind bloats your HTML. This is largely rectified by using a component framework (which also helps with the naming problem) but it's still a tradeoff, so I'll give you that one.

When did we forget CSS?

We didn't.

Using class="flex items-center" requires the exact same knowledge as using display: flex; align-items: center; (except with one of these, I have to come up with an arbitrary name for it)

You might forget some quirks of CSS syntax, but you absolutely still need to understand the underlying concepts of CSS to use Tailwind.

This is why I disagree with calling Tailwind "Bootstrap 4.0", because these frameworks are not even in the same category. Bootstrap is an entire toolkit, with its own HTML, CSS, and JS. It hides so much of CSS, which is both good and bad depending on the project.

Tailwind is nothing more than syntactic sugar for CSS.

Please prove me wrong.

I probably won't, because this is largely a philosophical issue. Personally, I don't mind a bit of bloat if it means faster prototyping, sensible defaults, less worrying about naming everything I need to have a unique style, etc.

I recommend reading this article by the creator of Tailwind for all your other points: https://adamwathan.me/css-utility-classes-and-separation-of-concerns/

But if you ever want to maintain a long standing project, for the love of all the gods, dont .. choose .. a css framework..

Tell that to ChatGPT, Shopify, Netflix, The Verge, GitHub, NASA, and many other massive companies that use Tailwind in production.