One thing that’s still unclear to me is whether you must disable this entry of about:config even if you go through the traditional privacy & settings drop down menus and disable the Firefox studies and usage stats options.

If the _only_ way to prevent having a remote entity modify your settings unannounced (even if not for malicious purposes) is to enter about:config and change app.normandy.enable to false, that seems like a situation where the absolute best case, most charitable interpretation is to call it an incredibly deceptive dark pattern from Mozilla.

This. After extensive reading about studies and Normandy here and elsewhere, I’m unable to find a straight answer about this. Does anyone know?

Studies and Normandy are different things, the former often using the latter. Only 'studies' has a checkbox in about:preferences, 'Normandy' is hidden in about:config .