This doesn't help at all. Diagrams are diagrams, what does it actually mean physically?
Think of it as similar to hi compression automobile engine (race car) being more efficient vs a low compression engine (tractor engine). Not exactly correct but a way of starting to think about it
Explosions release more energy in a shorter time, which leads to a higher peak temperature and thus higher kinetic energy in the products. This directly results in more pressure/thrust.