FYI: Diazo might still work on Volto. We are using server-side rendering. Diazo can take the HTML that is rendered by the node process on the server. The output can be transformed by Diazo. Just give it a try and let us know how it went.
I agree that we disagree on the Plone target group. I don't see how Plone can be a good fit for low budget websites and intranets. If a client comes to us with a few hundred or 1-2k Euros budget, I point them to wordpress.com and tell them they should not hire an agency. This is the best service I can do for them as an honest person.
There are some exceptions where clients need to use Plone because they are already using Plone elsewhere. In that case, Plone still makes sense and we usually sell them a theme that we used elsewhere or just amend a few colors and the logo.
We could sell them any Diazo theme that we hack together in one day. Though they wouldn't be satisfied with the quality and we wouldn't be either. This is not my way of doing business.
I used to do Diazo themes on the fly within 3-5 minutes on trade fairs, presentations or conferences. Of course, you can do a Diazo theme in minutes and you can accomplish a lot within a day. Problem is that a real-world website always takes at least a week in our experience. No matter if you have to build a theme from the ground up from a PDF you get from an agency, if you start with existing HTML, or if you build something on your own.
With Victor we are lucky to have one of the most experienced Plone theme devs I know in our kitconcept team, he knows Barceloneta in and out because he wrote it. Still, he always needs at least a week to build a decent theme. You are faster at the beginning with Diazo but at the end, building a Plone theme takes the same amount of time, no matter if you build a classic theme, a Diazo theme or a Volto theme. This is our experience from the past 10 years.
Plone and Volto are open source. You are free to enhance it to make it fit your use case. We are more than happy to help if you want to jump in. Please just keep in mind that you can not expect other people to work on a use case they don't have.