Probably everyone has heard of Gutenberg. It's the project name for the WordPress editor that shipped with WordPress 5. It's also known as the block editor.
The Beaver Builder plugin is compatible with the WordPress 5 block editor in the same way that it's compatible with the "classic" WordPress text editor. Depending on whether you set WordPress to prefer the block editor or use a plugin to maintain the classic editor, you can move text and images between Beaver Builder and the WordPress editor on a limited scale.
For more details see the detailed article about how Beaver Builder works with Gutenberg.
The responsive default heading and text styles that you can assign at Customize > General > Headings and Customize > General > Text in the Beaver Builder Theme apply as default settings in Beaver Builder and Beaver Themer layouts, but they also apply as default settings to headings and text in Gutenberg layouts, though they will not display until you preview or view the page.
We think Beaver Builder is far superior to the features that Gutenberg offers, but we encourage you to try Gutenberg and Beaver Builder for yourself. If you have a Beaver Builder license, you can download the current version of Beaver Builder from the My Account page, or you can install the free Beaver Builder Lite plugin.
Once you try both page builders side by side, we'd value your feedback on your experience. The best mechanism to get feedback directly to us is to submit a Support ticket.