The best defense is to have a product that's hard to clone.
If the only reason competitors aren't cloning your product is that they don't realize there's a big market for it, you don't have a sustainable advantage.
No, you don't, but you do have an immediate advantage, that can be used to establish a userbase and obtain other sustainable advantages before other players get involved.
Amazon's treatment of their smaller partners (Android, Basics) has not been ideal, fwiw.
If the only reason competitors aren't cloning your product is that they don't realize there's a big market for it, you don't have a sustainable advantage.