I found that the approach described only changes the published version of the page. The draft will still have the pre-bulk-update content.
Then next author to come around and attempt to edit the page will end up overwriting the bulk changes.
I tried to manipulate the drafts using methods available in the ContentDraftService using the following as suggested by Jonny in a comment response:
def draftService = ComponentLocator.getComponent(ContentDraftService)
But with this, draftService is a NullObject.
Does anyone know how to correctly get the ContentDraftService or have thoughts on what I found around what happens to draft when bulk updating via scripts?