How does gutenberg 2022 fit with themes offering a page builder

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WordPress

I'm a professional developer but a complete newbie to WordPress.

I've done a fair amount of reading, and I thought I had a clear mental picture of how plugins, themes and page builders relate to each other. I like to keep things simple and so had already made the mental decision that the latest Gutenberg editor probably feels like the most comfortable option for me. So I went in search of a theme to kick things off...

I found a list of the 25 Most Customisable WordPress Themes. When I started to read about these, I discovered that most seem to offer some kind of page-building experience, which is what I had already decided I didn't need, having played with Elementor.

I am once again struggling to see the overlap and separation between a theme and a page builder. Could someone point me at information that may help to clear up my confusion?

What I have tried:

Lots of reading and YouTube videos.