> but writing 500 meaningful lines to an existing 100k line codebase in a day is not easy at all.

I've had plenty of instances where it's taken more than a day to write /one line/ of code! I suspect most experienced devs have also had these types of experiences.

Not because the single line was hard to write but because the context in which it needed to be written.

Typing was never the bottleneck and I'm not sure why this is the main argument for LLMs (e.g. "LLMs save me from the boilerplate). When typing is a bottleneck it seems like it's more likely that the procedure is wrong. Things like libraries, scripts, and skeletons tend to be far better solutions for those problems. In tough cases abstraction can be extremely powerful, but abstraction is a difficult tool to wield.

The bottleneck is the thinking and analyzing.