+1 to csv_column. Only csv does not describe what the value field contains, which is the idea of the type 'field' (except for 'html' shortcut, which the given value is ignored)

About the value to pass, it cannot be optional for consistence with the rest. The link extractor is described using two required fields: type and value. And that cannot depend on the specific type passed. In case of 'html' shortcut, which does not need a value, it is ignored. But we cannot ignore the value in case of csv_column.