I've noticed that people can conflate "detailed spec" with "terribly meticulous process". Close collaboration with design/product doesn't mean that writing things down isn't useful, and can come in handy specifically:
1. When capturing complex logic areas, especially if related to any areas that are related to money or legal considerations
2. When onboarding new people on any side who need to learn about or get context on a product (product, design, eng)
3. When you revisit a V2 3 months later and forgotten what decisions you made or why you made them
Lots of detailed specs to me sounds like a fast velocity of products and totally compatible with startups. That said, you also added the word "lots" that OP didn't use. It could just mean two or three!
1. When capturing complex logic areas, especially if related to any areas that are related to money or legal considerations
2. When onboarding new people on any side who need to learn about or get context on a product (product, design, eng)
3. When you revisit a V2 3 months later and forgotten what decisions you made or why you made them
Lots of detailed specs to me sounds like a fast velocity of products and totally compatible with startups. That said, you also added the word "lots" that OP didn't use. It could just mean two or three!