I tried to add some points without duplicating any existing ones.Also, if you prefer a summarised answer(Not mine):Why stormtroopers always miss on imgur.com.
By 'Stormtrooper' you mean the shock troopers of the Imperial Army. We don't see the Imperial Army during Episodes 4,5 and 6 because there are no all out wars like during the Clone Wars. We almost always see the shock troopers (i.e. Stormtroopers). To answer your question:No. In fact, all Stormtroopers are excellent fighting machines. Wherever you see them miss, it was all intended. I need not repeat what countless other sources have already stated(You can find many other explanations).Try Wookieepedia
Stormtroopers, disparagingly referred to as bucketheads by dissenting citizens, were the elite shock troops in the Imperial Army, placed under the Stormtrooper Corps, the land-based forces of the Galactic Empire.They were particularly distinguished by their loyalty to Emperor Sheev Palpatine, the founder of the Empire, and were reputedly incapable of betraying either him or the Imperial regime.
Also we are told that they are better than the Clone Troopers we see during the Clone Wars, who had many a victory during the Clone Wars, even at great odds. Don't forget during the early years of the Empire, there were still many clones from the Clone Wars who were Stormtroopers.
The stormtroopers represented the ultimate evolution of the clone troopers, the soldiers who fought on the Galactic Republic's side against the Confederacy of Independent Systems in a prolonged and protracted conflict that came to be known as the Clone Wars.
Even though the Empire gradually lost its number of original Stormtroopers who previously were clones in the Grand Army of the Republic, most of the Stormtroopers we see in the movies belong to the 501st Legion(Death Star was manned mainly by them). They were Darth Vader's personal troops. He commanded the same men during the Galactic Republic as well. And only the best were promoted to this legion. Vader maintained the highest of standards.
The 501st Legion, also known as the 501st Battalion, was an elite unit of clone troopers in the Grand Army of the Republic during the Clone Wars
Stormtrooper cadets underwent extreme training for a really long time.Only the best were selected.The quality of the stormtrooper may have been reduced during the later years of the Empire. But even so, it would not be a good idea to assume that the small portion of Stormtroopers we see in the movies describes every other Stormtrooper of the Empire.
Unlike their predecessors, the majority of stormtroopers were non-clone recruits. Imperial cadets were shipped off to Imperial Academies, and subjected to rigorous training programs in order to produce highly trained shock troopers fiercely loyal to the Empire.
Among other things, cadets would train to fire blasters, learn to pilot Imperial walkers, and the ruthlessness it took to become a stormtrooper. Cadets who attended Imperial Academies were also forced to face programmable obstacle courses designed to test their strength, agility, reflexes and intelligence. Such courses and tests of skill became increasingly difficult over time, and accountability for losses were harsh.
While cadets attended the academy, they wore white uniforms and specialized helmets, similar to the standard stormtrooper or pilot gear. Aside from their basic training, many cadets were also assigned other non-combat duties on base. Such duties offered cadets the opportunity to gain experience over their peers, and were often presented as rewards for excellent performance during training exercises.
As cadets were being evaluated, the officers in charge were often instructed to take note of performance that might denote an affinity for the Force, and report it to one of their superiors.
I hope I brought something new to the table. Thank you.
