> Aside: Why are LLMs good at greenfield?

I have the complete opposite experience, where once some patterns already exist 2-3 times in the codebase, the LLMs start to accurately replicating them instead of trying to solve everything as one-off solutions.

> You can’t be inconsistent if there are no existing patterns.

"Consistency" shouldn't be equated to "good". If that's your only metric for quality and you don't apply any taste you'll quickly end of with a unmaintainable hodgepodge of second-grade libraries if you let an LLM do its thing in a greenfield project.