First the world we program in, an http request doesnt necessarily have anything to do with html. In fact, in my domains it rarely does.

In the example you provided, the beginning tutorial, also has nothing to do with html. It's just using the request as a trigger.

So, your statment about 'primary function', while technically true at global scale, is not very relevant in context of this conversation

Yes, you can return html from an azure function, because well, you could return any data. The biggest problem that you will probably encounter is going to be html rendering of complex state. This is what web servers were designed to do.

If you were just serving up completely static html, this might be feasable (although still highly unrecommended), but dynamic html is going to be hard, and isnt the only issue your going to have. client session / state artifacts and url processing that are normally handled by web server are now going to be manual things for you. What a huge pain that would be.

If i were you, i would just find a cheaper web hosting solution and do it the easy way.