Exo 2 font doesn't display

Noticed this while testing a premium theme, but it's also happening with Twenty Sixteen, Twenty Fifteen, etc.

Applying the Exo 2 font to either headings or body doesn't change the font to Exo 2; it uses the theme's default instead.

Reproduce the issue by applying Exo 2 to headings and body text in Twenty Sixteen or Twenty Fifteen, then trace the plugin's font loading and theme-style application path. Done means Exo 2 visibly renders in both areas instead of the theme default across the affected themes.

Written by the indexing model from the issue text.