I agree with everyone's evaluations and would like to add a comment of my own.
Professional quality lenses will show their value when you are pushing the edges of the envelope. Most mid-range consumer lenses will provide very good to excellent imagery when used stopped down a couple of stops from wide open and, in the case of zoom lenses; when they are not at the extremes of their focal ranges. It is absolutely amazing the quality that a person can get from low to mid-range lenses when shot, tripod mounted around f/8 or f/11 and at slightly less than their maximum or minimum focal lengths.
However, quite often lower cost consumer lenses cannot compete with professional high quality lenses in specific circumstances. As an example, I once owned a Tokina 400mm f/5.6 ATX telephoto lens which produced phenomenal image quality around f/8 or f/11. That lens could come very close to matching the quality of my present Canon 400mm f/5.6L. However, close only counts in horse shoes and hand grenades. The Tokina could not compete with my Canon when shot wide open which restricted the shutter speed I could use with that lens. The Tokina also could not match the instant and positive auto focus capability which makes the Canon 400mm f/5.6L a great lens for birds in flight images. It was not a cheap substitute for the Canon but, worked for me in a lot of venues.
There are a lot of other examples like this but, I will have to admit that many photographers are "overgunned" in the equipment department. A photographer who uses his camera to shoot pictures of the kids and Rover, The Dog, to email to the grandparents or who seldom prints anything larger than 4x6" (equivalent) images at the local discount store, very likely doesn't need top-line equipment. The prosumer grade equipment have wonderful capabilities.
A great photographer with a lesser camera/lens will beat an inferior photographer with top-line equipment. However, if two excellent photographers of the same capability are competing head to head; the one using the better equipment will probably come out with the best images.