Thank you for this! For anyone curious about more context, and what happens next, I'd like to share some here.

The goal of the "clickthrough" (aka parent-first) interface was to make it easy to select any layer of a block that features nesting. Consider the columns block, where you have to select individual columns to set their dimensions. With the clickthrough interface in place, it's trivial to dig through and configure each layer of a block. That's one example, but there is no limit to how deep a block can nest, and when each layer can have properties, it's important to think about how we can provide simple access to each of those layers.

Even if that interface probably still needs refinement — visual feedback, shortcut keys and the like — it's still definitely a layout first interface. Which is only one half of a block editor.

The other half is editing and writing, and unfortunately that experience suffered from the clickthrough interface. Being able to click the label of a deeply nested Button block and edit it is virtually unbeatable as far as editing templates, which are likely to grow in capabilities soon.

So, in the name of refining the clickthrough experience, it's good to disable it for now to give it more time in the oven. Those refinements are tracked in two tickets I'd recommend you watch if you want to follow along:

1. Visually indicate navigation mode, and make mouse accessible #17088, which suggests splitting the behavior in two tools, one (default) for editing, and one for layouting.
2. Create breadcrumb bar for selecting parent block #17089, which suggests introducing a breadcrumb bar so even if you never use the layout tool, you can still see the nesting hierarchy and click each layer to go to the block you want to configure.

@epiqueras There's something wrong with the milestones. Should that be 6.5? Its marked as "Future" (and some others too): https://github.com/WordPress/gutenberg/issues?q=is%3Aclosed+milestone%3AFuture