It’s bokeh, Kevin.
The term comes from the Japanese word boke (暈け or ボケ), which means "blur" or "haze", or boke-aji (ボケ味), the "blur quality". The Japanese term boke is also used in the sense of a mental haze or senility. The term bokashi(暈かし) is related, meaning intentional blurring or gradation. The English spelling bokeh was popularized in 1997 in Photo Techniques magazine, when Mike Johnston, the editor at the time, commissioned three papers on the topic for the March/April 1997 issue; he altered the spelling to suggest the correct pronunciation to English speakers, saying "it is properly pronounced with bo as in bone and ke as in Kenneth, with equal stress on either syllable". Source: https://en.wikipedia.org/wiki/Bokeh
It’s a large zoom lens Kevin.
The Sigma 150-600mm f/5-6.3 DG OS HSM Contemporary weigh 4.3 pounds.
The Canon EF 300mm f/4L IS USM Lens weighs 2.6 pounds.
The Canon EF 500mm f/4L IS II USM Lens weighs 7 pounds.
The Canon EF 600mm f/4L IS II USM Lens weighs 8.6 pounds.
The Sigma 150 – 600 is a reasonable weight considering its zoom range and the fact that Sigma is not associated with the main camera companies… they design their lenses for multiple mounts. Frankly, it’s a miracle of modern engineering that it’s only 4 pounds.
Oh and lets not forget that Sigma’s 150 – 600mm lens costs a literal fraction of both Canon’s prime and zoom telephoto lenses.
It’s called a monopod Kevin.
More mobile than a tripod while offering increased stability and lower strain on your body = monopod
You expect too much Kevin.
The Sigma 150 – 600mm is the ultimate value telephoto lens. It offers a wide zoom range, acceptable sharpness and clarity, for very little money. It is not meant to be this insanely, perfect, exceptional, lens. It’s meant to do a job and it does it well… Kevin.
Also, it could very well just be the copy he received… it happens. Even with modern manufacturing processes and extensive testing before ever leaving the factory… statistically for a lot of products somebody out there is going to get a dud. So Kevin’s sharpness complaint may be valid for his copy.