Altough I agree with jap-man san re: swinging bag is pushed than being hit. Some bags swing due to the amount of force that is thrown to it which it could not absorb. Thus absorbing excess force by swaying.
You could say I am old, but when the Ali-Frazer fight was held in Manila. They had a public presentation of their training retinue at the Folk Arts Theater. I was seated at the bleachers, a young boy, very excited. Mighty Joe started bag training with this extra-wide bag (oversized), as wide as him. He kept punching and hitting it with such power I could hear the swoosh of his punch and the smack from where I was seated. The bag did sway a lot. Similarly with Ali, the swoosh and the smack, wow, I will never forget that experience.
So, judge the strike by its penetration for me that is what matters. Penetrate the bag with your kick or strike this will give more power to the blow making it more destructive.
Practice is the key, begin light, gain control then move to heavy punching, look for depth (dig deep and deeper), then go back light gradually to heavy. Aim your strikes set up target points (color code if necessary) to help improve direction and technique.
Best wishes on your bagging.