Anthropic definitely takes the cake when it comes to UI related activities (pulling in and properly applying Figma elements, understanding UI related prompts and properly executing on it, etc), and I say this as a designer with a personal Codex subscription.

Codex does better if you ask it to take screenshots and critique its own UI work and iterate. It rarely one-shots something I like but it can get there in steps.

it's been frustrating how bad it is at UI. I'm starting to test out using their image2 for UI and then handing it to codex to build out the images into code and I'm impressed and relieved so far

Codex isn't great at UI, but you might find Gemini is competent enough as an adjunct. I've had some luck with that.