As someone who is dealing with this problem (27" 1440p monitor), I read that macOS renders the whole screen as a whole, instead of having a separate path for text. And there is a threshold PPI before it uses 2x assets. I had to use either a blurred rendering for bigger UI elements or the sharp, but small, representation at the native resolution. BetterDisplay[0] helped by tricking the OS to use the 2x assets at a smaller resolution. Still not as clear as my MBA's screen.
[0]: https://github.com/waydabber/BetterDisplay