1440p to 720p should be 100% sharp because it's integer scaling. Are the Mac display drivers garbage or something?
Well, look at it this way. How does 1280*720 look on a 27" display that you are sitting a 1-2' away from? That's right, it looks kind of crappy. I mean maybe if you can turn on HiDPI mode, see if that makes a difference, but at the end of the day...