There is no exact answer here, since you can talk about ESB as a specific design pattern, or as the discourse about the evolution of software integration tools and SOA.
ESB as a design pattern means that you manage communication between different services using a bus where clients can easily plug in and out. This is usually done by forcing them to use standard data formats and protocols, whereas with Hub and Spoke you might use custom connectors and data transformations for each client. This limits the number of problems you may have with running multiple integrations, but you may still have a single point of failure in ESB.
ESB as a discourse (or marketing term) is a more complex issue, where people argue over what is "True ESB". Some people say you need to have a modular architecture where you can select which components you deploy, or you need to be able to distribute the components across different machines to allow scaling and fault tolerance. In the extreme definition you would need to deploy even your data transformers as distributed services.