I was seeing significant performance issues using btWorldImporter on convex hulls.
It appears the problem is that btWorldImporter::convertCollisionShape(...) uses btConvexHullShape::addPoint(...), which recomputes the local AABB each time it is called, quickly degenerating into an O(N^2) operation.
My fix was to make btWorldImporter::createConvexHullShape(...) take the points/numPoints/stride parameters and pass them directly to the btConvexHullShape constructor.
Is this the preferred fix? Should I submit this as an Issue?