I've had the same experience as you did. When there's no type definition available, starting from an empty object quickly resolves a lot of the issues. But that really depends on the complexity of library you're trying to declare.

On the other side, I've also had cases when the type definitions were a pain. We have a web app and use .Net/TypeScript/React. We also use the commercial Kendo UI version. Since there's no versioning available (and the Kendo UI team doesn't seam keen on "type correctness"), we are (almost) always using a type definition file for another (newer) version of Kendo UI. We've had to "patch" the definitions on several occasions.