As Sally G. says, the Classic Editor does more than insulate one from the block editor. It also un-isolates one from the rest of the dashboard.

One of the stated goals of the admin redesign is to discourage different plugin developers from creating their own non-standard interfaces. Ironically the Block Editor is one of the worst offenders.
Instead of showing the common dashboard interface it completely hides it, making it difficult to find one’s way back after finishing a post or page editing task. (To be “fair,” when you’re in the Block Editor you can click the “WordPress” icon, which in every other context is the “visit the About WordPress” icon.)