Thanks for bringing a topic that keeps me awake at nights Justin. Because of the Gutenberg's limitations, 2 days ago I found another little trick Pattern developers are using to get around those limitations. This is more acceptable but unseasoned web designers are going to be perplexed if nobody explains to them what's going on:

This time, the example I will be bringing it's not from a theme but directly from the soon to be available - core patterns directory - Example pattern: https://wordpress.org/patterns/pattern/illustration-of-bird-with-callout/ .

Testing environment: WP 5.8 beta 2, Gut. 10.8.2

So this is the issue: The pattern comes with a button, if you want to add a second button, one would naturally press the inserter button and create a new button. The problem is that new buttons you create in this pattern will not look the same as the one that comes with this particular pattern. All new buttons will be pill shaped, as the pattern has a rectangular shape. It took me about 15 seconds to realize what is going on, and refusing to look like an idiot anymore, I checked the button's html code. Surely enough, they had hard coded the CSS code on how the button should look like.

At this point I had 2 choices:

Create a new button, switch to html mode, and add all the necessary CSS code for all the buttons to match, or the easiest method:
Duplicate the button that came with the pattern, and then visually edit the text and link of this second button.

If one does not realize what's going on, or does not know CSS, will have a hard time doing anything remotely useful things with these patterns, except simple text/images, etc... substitutions.

Finally you mentioned about the old-school purity of not mixing content and design is gone. Well, with it what's gone are parametric (advanced) searches, and front end editing. I can create a a Real Estate block that will hold all the information regarding properties, but there is no way to ask visitors to submit their properties from the front end, and even though I can search for a house in Los Angeles, OR a house with 4 bedrooms, OR one that costs exactly $1,000,000 (no ability for numeric comparisons here), but there is NO WAY I can ask the site to find me a house in Los Angeles, WHICH has 4 bedrooms, AND costs between $1m - $1.3 million.

For these 2 things (advanced searching & front end editing), you not only need to separate content from design, but your content must be structured, like using custom fields, so you can separate the text from numeric fields, and conduct these complex searches. Some things are simply not possible with Gutenberg, sometimes you have to do things "Old-School".

I think I just gave you a new post idea for next week... thanks for everything Justin.