Upscaling factor from 1080p to 1440p is bad, thus it will be blurry.
You can reduce the blurryness a bit by using AA.
Yes, it does not look that good, playing 1080p on 1440p monitor, but I do it too in order to get better fps.
Yes, it is blurry but not as bad as you think or as what people say.
BTW:
720p is not 1/2 of 1440p resolution but 1/4.