Well, I am not able to reach the benefits of this argument about how we should promote ease of use by exposing less features to users in the editor.

In the same paragraph, I read two contrasting sentences:
"For example, most users should have no need to adjust the line-height for their text."
(...)
"At a certain point, it is better to learn CSS."

How can the proposal of learning a code language, even if its basics, through CSS, be better as an solution for the casual users, rather than allowing them to simply choose a value in a checkbox?! By redirecting their actions to a specific field, requiring them to translate their thoughts into code, instead, at this age of even quantum technology, this argument is just an arbitrary decision for how to deal with their wishes. It is really not the only way for us to better serve the community.
Decades in programming have already taught developers how to organize complex code, and UX designers study decades to serve us very well to simplify these scenarios - where our arbitrary opinions clashes, there are methods out there with solutions for both of us.

Page builders come to my mind: most choose to not be complex, still have found a way to structure options. The most used page builder, at the time of this writing, Elementor, for example: its public are mostly casual users, because of its ease of use, compared to other page builders. And all of the CSS options are there through countless options. Yet its interface is simpler than ours in Gutenberg.

There is a reason to why Microsoft word, these plugins and such have become famous. And all of them are way more filled with options than the most bold idea for Gutenberg.

What you envision is a better solution for some of us, for sure. Those that are able -and prefer- to achieve their content and design goals faster and freely from CSS code. But not casual users.

Casual users are not users unable to deal with options. They are People, therefore they have diferent wishes, which one day Will require the option we may choose to hide, because we thought they wouldn't ever need. CSS are the basic options (For us in code. Why not for them in design?). People are going to avoid what they do not need at the time. And what for them or for you is unnecessary, for another casual user is as necessary as a drug. These little options are what people rely for content creation.

Gutenberg has a complex goal - many holes in the foundation is a rule or should be an exception?. What you propose is exceptions in the Foundation.

Imagine if tax payers needed to learn code in order to answer urgent requests instead of on their mother lamguages? It could be better for those managing the requests? Okay, but better for everyone? No... out of scope.

"We certainly cannot expose every possibility via an option."
It is true that we cannot expose every possibility via an option.
But it is false that we ...Certainly... need that.