If you send the lens in, they will test it under in a controlled situation to evaluate and diagnose the problem. If it meets specifications, they will send it back to you untouched. In the meantime, you could have done a more scientific analysis of the problem and saved yourself the problem and expense of returning the lens.
Looking at a picture with a mixed scene and lighting, without knowing the EXIF data and whether or not a tripod or a filter was used is not very scientific.
You have opinions stating this image appears OK and others that say the left side is out of focus.
My advice is to do more testing. Here is a link to a sample chart and the methodology.
lens chart
There are many other charts available on the web.