Whenever nested calls to the_content happen in Gutenberg, the editor is outputting paragraph tags all over the place.
Gutenberg
The Limitations of Gutenberg
So, I’m actually really enjoying the editing experience in Gutenberg. It’s really, really well done, especially considering what a mess the process looked from the outside. But it has limits.
Thoughts on Gutenberg
Gutenberg is likely going to help the WordPress system enormously, but until it does, it’s going to be a burden for everyone.