> 1) I occasionally have to use gimp on OSX, which has an absolutely broken focus model. Click-to-focus means that if you want to (for instance) select the crop tool and then use it, you have to click on the tool palette to give it focus, then click on the crop tool, then click on the image to give it focus, then click on it again to start cropping.
Of course that isn't an actual feature/brokenness of MacOS. Ever since near the very beginning, there's been a concept of a "tool palette" which floats on top of other windows, doesn't accept focus, and accepts clicks even when not focused. Photoshop's tool palette certainly used to work like that many many years ago. (I haven't used it in a decade or so; not sure how it works now). For a built-in example in OSX, look at the standard font window.
Maybe *GIMP* on OSX is broken in this way (don't know; don't use it either), but you can't really blame OSX's focus model for GIMP being a terrible port.