Most function keys (physical or not) suffer from a lack of “findability”.

When a touch typist learns QWERTY, Dvorak, or some other keyboard layout, the exact location of keys is burned into their brain. This is why I can put my hands on a keyboard in the dark and start typing comfortably.

Function keys lie outside the scope of these well-known layouts, and aren’t something that most people commit to muscle memory. This is why I can never find the backlight controls on my 2014 MacBook Pro in the dark without fumbling with the screen brightness, audio controls, and app switcher buttons.

Yes, it’s possible that the Touch Bar is worse than the status quo, but the status quo was already lacking.