This is what drives me nuts...designing themes for both the Classic editor and the block editor, only to later find out things were completely changed.

Then there is the issue of trying to get the front-end styles into the block editor is an absolute nightmare (I often invent new swear words). For example, try changing the main content font size when the block editor is loading its own CSS in the footer area; overriding what you try to do.

Styling for the classic editor is a breeze! If the dev team can find a way to make it as easy as the classic editor, I would be happy as can be!

The dev team makes these changes that will affect millions of users who have themes (and plugins) which need updating constantly is taxing. I feel sorry for the theme authors/shops that have a LARGE portfolio of themes and plugins that were updated for GB compatibility. Luckily, I'm keeping mine limited...less overhead when it comes to constantly changing and updating themes.