@toast19 Packs transfer more weight to the hips if you have a hip strap. This takes load off the back and core and is less tiresome than using a vest. Packs are efficient for moving things on your back. Vests are not. A vest of the same weight will be a harder workout.
@toast19 A vest won’t change your center of gravity much. A pack will push your center of gravity further to the back. You can carry much more weight with a pack than a vest.
If you run out of space in your pack and want more weight, you can always use a vest and a pack together.