It's amusing to think that claude might be better at generating ascii diagrams than generating code to generate diagrams, despite it being nominally better at generating code.
I'm generating a lot of PDFs* in claude, so it does ascii diagrams for those, and it's generally very good at it, but it likely has a lot of such diagrams in its training set. What it then doesn't do very well is aligning them under modification. It can one-shot the diagram, it can't update it very well.
The euphoric breakthrough into frustration of so-called vibe-coding is well recognised at this point. Sometimes you just have to step back and break the task down smaller. Sometimes you just have to wait a few months for an even better model which can now do what the previous one struggled at.
* Well, generating Typst mark-up, anyway.
I just ask it to generate mermaid diagrams, which are just code that you can render using the mermaid diagram website