A system is an assembly of components with effects outside the scope of any one component. These effects are due to interactions between components. This is why we think of systems as synergistic entities with emergent properties.
Anything worth devoting significant time to learn is likely operating under system effects. Therefore, effective teaching must abide by some underlying principles of systems.
In other words, great teachers are more than system thinkers. I say more because effective teaching is the result of at least systems thinking as well as psychological phenomena such as accounting for and influencing learning behaviour.