you just write in Markdown (the same thing Lemmy uses), pick a theme, and you’re good to go

That is far too basic for most websites. It’s absurd to suggest that’s a valid alternative for something like Wordpress + Elementor.

Squarespace should be on the table for static websites as well.

How so? It’s not static that I’m aware of, unless you’re exporting it to a file after using the UI to create it?

I assumed we were talking about direct replacements for WordPress, not hosted alternatives.

Well, as you said, Wordpress does a lot of things. Shopify, Wordpress, Squarespace, etc., are certainly interchangeable/competitors to a large degree. Wordpress has hosted options and is a default/main option for many hosting companies.

You can build a full website with every major function and design option with Wordpress. You can’t with Jekyll and Hugo unless you can code.

static site? - Hugo, Jekyll, etc - just generates regular HTML

These are either vastly more limited, or they require you to be able to code.

ecommerce? - consider nopCommerce or OpenCard

I’ve never heard of these, but I have seen people say that if you want to do ecommerce you should only use Shopify, because even small differences can result in people not purchasing your products.

What would you use instead?