If the ContentEntityObject is going away, that’d be news to me. But you don’t have to use the space.Spaces object. You can use the ContentEntityObject directly.
Please see my response to the question How to get Last Modified Date of a Confleunce Space programmatically? for the last modified date.
For getCreator, I’m not sure. That new way of getting spaces and content needs waaaay better documentation than is out there now.