In Illustrator:
To set the default font you need to change the New Document Profile that you use to base your new documents on, like Print.ai, Art & Illustration.ai, Web.ai.
Open the profile you want to modify from:
Mac: (User)/Library/Application Support/Adobe/Adobe Illustrator version number/language folder/New Document Profiles
Win: C:\Users\....AppData\Roaming\Adobe\Adobe Illustrator version number Settings\language folder\x64\New Document Profiles
Open the Window > Type > Character Styles panel.
Double click the [Normal Character Style] and change the font in the Basic Character Formats.
Save the file.
In InDesign change it without any documents open.