Currently, GetItems (specifically, for SharePoint) does not support selecting fields to be returned. Moreover, many fields are being returned as expanded properties. For, example, Created By or Modified By each return 5 properties. As a result, for a list with many fields and many items the payload becomes huge. The very slow action - Select - is needed to get only what you really need.
Suggestion: Add option to select returned fields for GetItems action. It's a standard for all the "legacy" worflows.