Games

Scale absolutely matters, but the scale of the new game screen is (or should be) very minor compared to the game itself. That one scene should only be setting the variables for new play, not interacting with anything outside of it.

And, to be clear, the main concern is simply the input handling in that scene. The UI itself doesn't really need to be changed, just which buttons change the highlight focus.

I can imagine it was likely thrown together quickly, perhaps with some unnecessary coupling, or maybe reading the inputs using action names that also relate to gameplay, so it becomes awkward changing it out.

I'm not so experienced with Unity, but in UE and Godot, adding and mapping inputs is fairly trivial - select the "up" button and map it to "ui_focus_up", etc. I can't see it being much more complex in Unity.