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.