Haven't watched the video, but what do you think circularization is? If you're “just a circulization away from orbit”, you are indeed going a bit slower than orbital velocity. There's no point to going orbital velocity if your trajectory still brings you back inside the atmosphere. To get to orbit you want to raise your periapsis outside the atmosphere, and you do that by doing a burn at the apoapsis, which is what we commonly call "circularization".