Market exists: Obsidian has 1M+ users, Typora is popular, iA Writer has a loyal following. These aren't VS Code users who wandered off — they're writers, PKM enthusiasts, and note-takers who find IDE-style editors overwhelming for prose.
Different audience: Developers might prefer VS Code + Markdown Preview Enhanced. But Ferrite targets people who want a focused writing tool, not a general-purpose editor that happens to support Markdown. Think "writing app" vs "code editor with Markdown support."
Native advantage: Most Markdown tools are Electron (Obsidian, Typora, Mark Text). Ferrite offers instant startup, lower RAM, and native performance — appeals to the "I want my tools to feel fast" crowd.
You might be right that it won't achieve mass adoption. But there's a niche for "Obsidian but native and lighter" that I think is underserved.