The word “rant” is a lightning rod to draw the hosts to your post. You don't want that.
Apple never designed any version of Pages over the years to compete, or clone features found with Microsoft, or any other vendor's word processing application. So watermarks are something you normally create elsewhere and drag/drop onto Pages before moving them to section master.
The following AppleScript is limited by Apple's scripting definitions for Pages, so the best it can do is to automate creation of a watermark up to an intermediate stage, and the rest is user interaction with the application.
Tested with Pages v5.6.2 on El Capitan, and v7.0.1 with High Sierra 10.13.5.
set watermark to "Draft"
tell application "Pages"
activate
set newDoc to make new document with properties {document template:template id "Application/Blank/Traditional"}
tell newDoc
set locked of every iWork item to false
tell current page
-- a 4 x 6 inch (288 x 432 point) box with left upper corner at 1.25 x 3.5 in (90 x 252 point)
set thisTB to make new text item with properties {height:288, width:432, position:{90, 252}}
set object text of thisTB to watermark
set opacity of thisTB to 15
set rotation of thisTB to 45
tell object text of thisTB
set properties to {font:"Helvetica Bold", size:120, color:{0, 0, 0}}
end tell
end tell
end tell
end tell
And the resulting Pages document looks like the following:

Now, you must do the following manually:
- Arrange Tab
Set Text Wrap to None
- Text tab
- Click the center text button for Text horizontal alignment
- Click the center button for Text vertical alignment in the Text box
And finally, Arrange menu : Section Masters : Move Object to Section Master.
You can copy/paste the Text box from this document to another, providing you use Paste, and not Paste and Match Style in the destination document. You can export to PDF, and drag/drop the PDF into future Pages documents for use as an object section master.