Agreed, if you have a dedicated engineering team, but most non-tech companies that need basic websites don't...so in that context, Wordpress's admin UI is a big gain. It's familiar to users and provides media management functionality out of the box. The vast majority of CMSs have terrible/non-intuitive admin UIs and limited functionality. Leaving aside Gutenberg and the rest of the garbage pile that is Wordpress, the admin is the primary selling point of Wordpress IMO.
Things like copy/paste from Google docs with keeping all of relevant the styles and links works. And I guess that a bunch of users is doing that - using WP as a platform for distribution of content.
Having a classic editor plugin has nothing to do with characterizing people as crufty throwbacks who can't learn new things. Many people are in the business of their business and don't care to learn the next new-greatest-software every few months.
Especially when you add custom blocks specific to their site needs
Take a look at WooCommerce. I guess that it is much easier to do some of the custom code than to reinvent a wheel. Not to mention learning users on how to do something in a totally different environment.
The designer can, within the structure and strictures of Wordpress, build a site with all the whizzy things the client wants, and they can charge $X for it. A developer can do all of that as well, but they will probably need a designer as well (see above parenthetical), and it will cost $X * 2.
The counter to that is, "well, just build a good templating system and tweak that for other clients, and you're good." Which is true, and that's why there are lone PHP developers out there who make a decent living with a stable of clients.
One of the worst aspects of Wordpress is dealing with the infuriating and opaque reasons why a particular site is slow. A relatively simple site can be maddeningly slow for any number of reasons, and finding them is like searching for a contact lens in a full bathtub.
If performance is a real business concern (and when is it not?), hire developers, not designers.
Hire developers, not WordPress developers. Because the latter will push WP onto a project where clearly the downsides, like performance, outweigh the benefits. But the latter may pick WP when it is a good fit.
I mean, I get it. I've written some stuff that screws the pooch performance-wise, and the solution isn't immediately clear. But with WP, and with enough installed plug-ins, the reason for the slowness may simply be "in order to work with WP, there is a lot of back-and-forth with the DB amongst all these plug-ins," and there ultimately isn't anything you can do about it.
WP is amazing that it does so much and works as well as it does, but let's not pretend it's not a bit of a faff sometimes.