I focus on SEO. That said, I can create websites in HTML5 and CSS3. In the last year I have also spent a lot of time modifying WordPress themes.
I never liked Elegant themes. They are beautiful themes but funky. It's like Elegant doesn't give 100% theme design for free. There's always something you need to buy. That said, Divi is beautiful, but it too is a little funky. The demo has a lot of animation which makes it jumpy and a little slow.
Page speed is an SEO factor.
The Genesis framework is built for SEO. Those guys are SEO geniuses. But if you use the Yoast SEO plugin (free version is enough) you will have serious SEO help on any WordPress theme.
LayersWP looks interesting. I don't need drag and drop but I might check it out myself. Their demo page is not jumpy nor slow. Doesn't look like its a framework like Genesis, more like a theme you can modify. That is, it doesn't have a built in SEO piece like the Genesis framework. But again, get Yoast.
Finally, with the Genesis framework you will still need a theme, and now you'll need a Genesis theme. Not real thrilled with Genesis themes. Design is not their forte. They are SEO.
Hope that helps. It was a good question. You are on the right track.
Not sure what "theme-locked" means, exactly. I just skipped that part of your question. Forgive me.
If you'd like to talk more just call.