I would maybe argue that there is a sweet spot of how much you feed in (with some variability depending on task). I tend to keep my initial instructions succinct, then build them up iteratively. Others write small novels of instructions before they start, which personally don't like as much. I don't always know what I don't know, so speccing ahead in great detail can sometimes be detrimental.

Agree. I don't use term "spec" as it was with "spec-based development" before llms. There details were required to be defined upfront. With LLMs you can start with vague spec, missing some sections and clarify it with iterations.

Sweet spot will be a moving target. LLMs build-in assumptions, ways to expand concepts will be chaning with LLMs development. So best practices will change with change of the LLMs capabilities. The same set of instructions, not too detailed, were so much better handled by sonnet 4 than sonnet 3 in my experience. Sonnet 3.5 was for me a breaking point which showed that context-based llm development is a feasible strategy.