These look good to me!
Could we also add support for loading separate styles for rendered-blocks only?
In WP 5.8 we didn't do it because there were no block themes, but in 5.9 where we'll also have a check about whether a theme is block-based or not, we should default to loading separate styles for block themes:

// Opt-in to only load styles for rendered blocks.
add_filter( 'should_load_separate_core_block_assets', '__return_true' );

Note that this is currently done manually in the TT2 theme for example, and it should be the default out of the box

Excellent. We should probably do an issue to keep track of what would be good defaults. Most of these features have been rolled out incrementally and opt-in, as things get settled, good defaults are crucial.

Just personally I appreciate this, as it furthers the thing I've appreciated the most about developing a new theme: all the complexity and boilerplate code that's beeen absorbed by the system, rather than being something I have to shepard along from theme to theme.

In addition to those mentioned, I have automatic-feed-links (https://codex.wordpress.org/Automatic_Feed_Links) as well.

I do wonder if we can't remove wp-block-styles from the list, though. This one opts into the extra theme.scss styles, which provide a handy shortcut for themes being upgraded to support the myriad of new blocks without having to provide new styles for each. However as you are starting work on a new block theme, and especially as some of the properties currently stored in theme.scss can be absorbed by theme.json, this one might likely end up unnecessary. And you can easily opt into that one separately as well. What do you think?

Updated this:

• Added the styles optim.
• Added the automatic feeds.
• Removed the wp-block-styles.

Sweet!

@youknowriad I realize the following use case is not something to cater to, as I'm fully aware of how hacky and temporary it is. However in case it has legitimate side effects, I wanted to share.

Until I can fix them at the source, I'm loading a low-specificity stylesheet into the editor, like so:

add_action('init', function() {
	wp_register_style('editor-hacks', get_template_directory_uri() . '/editor-hacks.css');
 
	register_block_type('mocco/editor-hacks', [
		'style' => 'editor-hacks',
	]);
});

As of this PR, that file no longer gets loaded at all. I checked to verify that the commit before this worked fine. Can you tell if this is just me doing it wrong (very possible since I know it's hacky), or whether there's a legitimate issue here?