Both. And internal tools. And infrastructure scaffolding a la terraform. And visual design.

And frontier models routinely crush all the above in a way I couldn't, at speeds unattainable to mere flesh and blood like me.

Not the guy you asked, but honestly, I'm not sure which one of those I'd consider better use cases, not worse.

Generally end-user applications, depending on how you classify internal tools. I'm generally very happy with the output of Opus 4.X with a moderately structured CLAUDE.md and some investment in detection/avoidance of anti-patterns (Next.js+ts). I imagine that the bitter lesson is true here, and these heuristic guidelines will become increasingly unnecessary w/ smarter models.

Library-type work has mostly been side/toy projects, although fwiw, with a standard/spec on hand (CommonMark for example), I'm also happy w/ the output. It's often possible to "close the loop" and have the coding agent autonomously iterate until the standard is adhered to.

Judging by parent's CV, it kind of looks like they are relatively new to the industry and working in areas where they are heavy on the greenfield side of the equation. I get the sense that they've probably had some good success on smallish projects where they are in charge of keeping it all in their head. That's not to say that isn't earned or otherwise valuable experience, but it surely is not the way a lot of software projects are situated. Parent: I hope you won't take my comment here as a slight. I mean no offense, just pointing out what I think is probably valuable context.