The font-size seems to be set to "small" system UI font, which is smaller than both the main menu font and e.g. Finder's file list. The standard size should be preferable. That should (IIRC) also scale if users change their system font size to "larger". (It's worse than iOS's dynamic type features, but it's something.)
On a non-retina 1440p screen, you can see how smol the tab font is in comparison to other UI elements on screen: