All of these look quite terrible to my eyes. None of them really resemble the classic AI slop landing page, either (of which this [1] is a decent illustration). I'm no huge fan of that style, but it's at least readable and functional, and thus better than the results you got by a mile.

It seems like you were starting with an existing HTML file you asked it to redesign. Generating from scratch with strict guidelines could be more representative.

[1]: https://vorpus.github.io/performativeUI/

Agree. I find this route reliably produces better results. Not sure I understand why though. Intuitively I'd think the models would be able to do approximate designs with higher fidelity using code as the primary reference.