FWIW most LLMs are pretty terrible at estimating complexity. If you've used Claude Code for any length of time you might be familiar with it's plan "timelines" which always span many days but for medium size projects get implemented in about an hour.

I've had CC build semi-complex Tauri, PyQT6, Rust and SvelteKit apps for me without me having ever touched that language. Is the code quality good? Probably not. But all those apps were local-only tools or had less than 10 users so it doesn't matter.

That's fair, I've had similar experiences working in other stacks with it. And with some niche stacks, it seems to struggle more. Definitely agree the more narrow the context/problem statement, higher chance of success.

For this project, it described its reasoning well, and knowing my own skillset, and surface level info on how one would start this, it had many good points that made the project not realistic for me.

Disagree - the timelines are completely reasonable for an actual software project, and that's what the training data is based on, not projects written with LLMs.