While working on this though, I realized that iPhone keyboard is “broken” on deeper level than just the Shift key visual design. And this issue exists since original iPhone OS.
You see, when you tap the Shift key, nothing else changes except the Shift key. No other key is visually changed, but the result of tapping any of the letter is changed.
As Vacić goes on to say, it isn't so much that the shift key is broken, as it is that the shift key doesn't really shift anything. Yeah, yeah, yeah, a physical keyboard doesn't work that way either, but if an implemented shift key actually shifted keys from lower case to upper case I know I'd be a happier iOS typist.