The lens has a problem! It should be sharper at wide apertures than it is at f/10. Send it back asking them to fix it or replace it.
You can see the combined results of testing this lens by many users here. Note, this curve is not the one given by your software, but is normalized. there is no big dip at f/5.6, but there is a small one, and that might be caused by just a couple of lenses. I'm sure that any obviously bad ones were not included in the summary. You can't compare it with a different lens, each one has its own curve.
The tests done by photozone are here: Note, f/10 is always the lowest resolution point when compared to wider apertures.