It seems that knights serve in a "shock troop" role something that broke the stalemate of a battle by introducing a decisive factor into the mix. My lecturer speaks of them as something entirely new and completely changed the battlefield and as a result the social orders of the time period.
No, your lecturer is repeating outdated scholarship that's long been surpassed. The concept of an armored heavy cavalryman (knighthood as a social class was not yet developed) wasn't an innovation to the medieval battlefield. Medieval warfare, contrary to popular belief, was not dominated by heavy cavalry and "knights" were not exclusively mounted troops.
The idea of heavy or "shock" cavalry wasn't really new or revolutionary. Various types of heavy cavalry had been in use since at least the time of Alexander the Great. There was a long stretch during the era of the Roman Empire that was dominated by infantry, but they still used armored horsemen and towards the later Empire era they began to fold in allied units of heavy cavalry. The Arab Muslim armies also used them heavily, which is one way the idea was re-introduced to the West. The Battle of Tours and Charles Martel's subsequent creation of his own heavy cavalry force is sometimes credited as the start of the "Western knight" idea.