A workspace for the plan, a studio for the prose.
Notion shines before and around the writing: the character database, the timeline, the wiki of who knows what. Many writers plan a whole series in it and never want to give that up, and they should not have to.
The writing itself is where the fit gets looser. Notion is built from blocks, which is wonderful for structured documents and awkward for the long, unbroken flow of a scene. DraftProse is the opposite: a quiet, continuous page made for drafting prose, with the structure held in a binder beside it.