Hi waaaghpaint,
Thanks for posting in Apple Support Communities.
You can set the default font in pages to set the font size to 11 without it reverting.
"The font and font size you choose apply to the Body paragraph style. Other paragraph styles use the same font, and their sizes adjust according to the font size relationships of the original template. For example, if you choose Lucida Grande and 12 points, the Title paragraph style in the Blank template uses Lucida Grande and its size is 33 points instead of 30 points.
- Choose Pages > Settings (from the Pages menu at the top of your screen).
- Click General, then select the checkbox next to “Set font and size for new Basic documents.”
- Click the Font pop-up menu and choose a font.
- Click the arrows next to Font Size to choose a font size, or type a value in the text field.
- Click OK.
After you make the update to the setting, it applies to any new documents; it doesn’t change the font for existing documents. If you later want to revert the templates to their original fonts, deselect the “Set font and size for new documents” checkbox."
These details can be found in Set a default font in Pages on Mac - Apple Support.
Regards.