Can someone please help me understand why people are obssessing over this as a Figma killer and not, more clearly, a shot at Replit, Lovable, etc.?

The AI app builders are part of the AI economy already. They are essentially re-selling tokens/compute. It's an existing horse race.

Bringing a Figma killer to the market is converting a conventional software sector into an AI one. So it's more disruptive.