Well, nobody is going to say that lens is soft at F2 - pretty sure about that.
I don't believe you wasted your money and bought the Nikon version of this lens when the Sigma is available at nearly 50% off. I bet if you didn't look closely, you couldn't tell the difference on prints.
(I kid, I kid - but hopefully you get my point.)
I can shoot at 2.8 with my 70-200; I can't do that with the 18-200,and yes, that makes that much difference to me, as I'm always fighting for more light. Not to mention the subject isolation, bokeh, and contrast shooting at 200mm/2.8 gives me.
I'm happy that you enjoy your 18-200. I hope you have many more years of great shooting with that lens. Please share some of your favorite images with us!
I hope you wish the same for me with my 70-200/2.8, rather than accusing me of pointless pixel-peeping.