I think You are using missleading class names.
There is class TaskHandler that is responsible for parsing node xml.
There is class WorkItemHandler that is used for executing actions that developer can assign to specific types of nodes. This is if I understand right. Or mabe only for human tasks?
And now there are many classes that extend WorkItemHandler but are named *TaskHandler even if they have nothing to do with TaskHelper class. Its hard to read developers intentions when reading API and the source code.