Sorry... I lost my text and couldn't edit any more.
The first shot shows a major limitation of this lens, which may or may not be a concern, depending on your purposes. This shot of a flat granite wall was taken at f/2.8 facing dead-on. Fully open this would look atrocious. I'm not sure how this compares to the other lenses included in your analysis. For pictures of a flat artwork in a gallery in very low light this could be a critical issue. Or for taking pictures of the night sky.
The second two shots show a more typical use for this lens (stopped way down to f/8 or so), and under these conditions it has performed admirably for its cost.
Another application where softness wide open has been less of an issue is when taking portraits from very close up (like a person sitting across a table from you). In this situation the person's face is generally in the center of the frame and is in sharp focus, while the surrounding back/foreground is OOF anyway and doesn't reveal the soft corners as badly.
Some things to consider!
Yours, etc.,
Don