In reply to Bastian.

How do you have a business without some kind of management plan with your clients whereby you'd be able to get paid when they are fixes necessitated by core/them/plugin changes? I suspect that most Gutenberg haters are people who spend more time talking trash on the internet than they do making sure their work doesn't get left behind when to world changes.

The web is fluid, your work product shouldn't be stuck in a time capsule.
It's your job to explain this to them. If you can't paid maintain you're work then you are getting the short end of the stick. If you can't keep your clients website's working they will find someone else who can.