“This also greatly reduces the complexity of activating a theme, you look at the demo, and then you choose to activate or not.”
This is simply not true. A site can have features that you can only see if they look good on a particular theme when tested; also, as I already reported, in some themes there are bugs that do not appear in the demos.
Regarding the theme you reported several months ago, that one is not one of the newer ones made of pure blocks. The new block themes are made up of components that can be arranged in many ways, and that’s done at the content level. We have templates and what not available, and you can modify those as you’d like.