While I do wholeheartedly agree with everything you wrote, I still feel need to point out a limitation I don't see (or feel) solved: how do you scale this approach to n>1 developers? In a large brownfield you can assign quasi-solo projects in different corners isolated by sufficiently wide buffers of legacy code you won't touch, but a multi-developer greenfield needs architectural structure simply to give the parallelly written code something to integrate with.
In one of my previous jobs we faced this issue, and we've approached it like this: we would start with a design meeting for a simple solution, divide it up into pieces that can be worked on independently, with agreed-on interfaces. Then each of us would be working independently on their piece, and we'd revisit the design questions as issues cropped up. Is this the best approach? I don't know. But I don't think it's bad.
