In a sense, this replaces the need for theme templates (templates within the templates folder). Block Patterns are basically presetting a layout where you insert elements (content) into your post/page via filling in the blocks.

I'm really curious how this will affect theme marketplaces like Theme Forest. I've brought this question up many times in the past about the direction WordPress is going with the block editor...actually, it's not really an editor, it's a page builder!

...anyway, no one has really answered the question of what is going to happen to the 1000's of themes on marketplaces like TF, and others?

I also predict third party page builders are going to be obsolete despite what some are saying. With a business and investor mindset, if you were the big-wig of WordPress, wouldn't you like to take out the page builder market and grab it for yourself?