I think you are spot on with your reflection on the struggles between hyper-focus and inter-relations between some of the present work in phase:2. We have projects underway that are both ambitious in scope and have considerable dependencies between each other. In the end, as you well mention, it all needs to come together into a cohesive user experience, which is what matters the most. It's tricky, for example, to release global styles without many of the pieces from site editing that allows for it to make sense. However, several specific design tools that are rehearsed and stressed through global styles can and are released independently in specific blocks but with less fanfare. (There are several additions to block features in 5.6 in that sense.)

Ultimately, the balance between getting things out there as soon as possible to gather broad and meaningful feedback, while ensuring we are shipping things as ready as possible, is an ongoing product challenge. I think it's important, though, to try to release things as soon as possible as the contrast with real usage is always invaluable for the project as a whole.

I think it's also worth saying that, while the site editing projects advance little by little together in the plugin, there are many other parts that do make the light of day, large and small, int he major WordPress releases — like Patterns, which was released in the previous major version and includes several improvements already in 5.6, or the block directory integration. The same can be said about the block editor itself, which includes hundreds of substantial improvements from major release to major release.