They are trying to push forward with what they think is a good idea, and best for the products future. Doesn't mean they're right, however there is the argument that the customer doesn't know their experience could be improved.
Time will tell in the WordPress case.
It can be good to recognize that back-compat has become detrimental. When that happens, you need to communicate the reasons why you have decided to break it and communicate that the projects values have changed going forward. It doesn't sound like either of those things have happened here.
I say this as someone who loves WordPress and has been developing on it since 2006. I’ve also been working in UX and UI for ten years. I’m hoping for the best, but bracing for the worst.
Gutenberg from my experience is a server hog compared to the classical Wordpress. It's harder on database servers and on memory. Yet they won't even change their PHP practices to make it 7+ requirement.
AFAIK there is no change to database or memory usage post-Gutenberg, especially since pretty much all of the new code executes on the client side when you edit a post. It may use more memory in your browser, but not anything that should cause issues.