Thousands of deer are killed with buckshot each year and have been killed this way since the 1700s when deer hunting with dogs got popular in America...
The trick is to test your gun with different brand shells and chokes at different ranges...Once you find a load that will put several pellets into a 8-10 inch circle at a given range then you have determined the range limitations of that gun...Then you must limit yourself to that range...
Where some have problems is not checking their guns and shooting too far...This is no different than the rifle hunter that goes hunting with a bore sighted rifle or shoots at game at ranges too far for his skills...Buckshot itself is very effective if used properly...
Hunters that dog hunt post gunners at known deer crossings...When a deer comes by the hunter shoots 2-3 times as the deer runs by...This is alot like wing shooting, some are very good at this, some are not...I've had deer drop at the first shot and some continue on...When properly hit with buckshot the deer doesn't go far...Since the deer dogs are close behind they continue on the track and find the deer usually laying within 50 yards of the first shot...
This is how buckshot is used effectively...In a still hunting situation I prefer a single projectile and a gun with a scope to help with low light situations...