I own a S4 and I am not experiencing any of these issues. The last update fixed the "high quality" issue where it wouldn't even upload your picture, instead it uploaded a notebook paper looking thing. Weird. But I have high quality checked in the settings and it uploads just fine for me.
I know personally I don't use the IG camera. I have that option unchecked. So when I choose to upload a picture to IG I can either choose from my gallery or choose to take a picture with the S4's stock camera. Even when cropping it comes out fine as far as quality. The only annoyance I see is that portrait pictures seem to be in landscape mode. I noticed this on a test picture. But quality was always there.
Nexus 5 White