The laws of physics along with your anatomical structure plays a role in comparing ankle weights and weighted vests.
Your center of gravity lowers when you add ankle weights to your lower body. Your body’s anatomy is structured around your center of gravity being close to your waist line. Women naturally have a lower center of gravity than men partially because of larger hips and smaller upper body frame.
Accumulated fat could change the center of gravity as does building muscle mass.
Regardless of how you change the center of gravity, once the center of gravity shifts, it places un-natural load on the muscles that keep your core in balance.
Without training, you risk injury to your core muscles when you shift the center of gravity. Gaining additional fat or building muscles is a gradual process which allows your body time to adjust. Adding ankle weights shifts your center of gravity quickly.
Add to the ankle weights the momentum of speed training and you have a recipe for disastrous damage to the stabilizer muscles of your core including those in your lower back.
A weighted vest is a much safer way to increase both caloric burn during workouts and your over all cardiopulmonary strength.
Weighted vests work with harmony with your body design which is to retain the center of gravity close to the waist without hindering the movements of your limbs. There is a reason that your hand are smaller than your chest and your feet are smaller than your thighs.
Part of that reason is the anatomical connection in your muscles and the lever systems are built to allow your hands and feet to move fast and your trunk to move slower while carrying your stable core.