So the hand moves roughly the same amount for both Bedrock and Java but the difference is Java has a "scale" for how much it moves whereas on Bedrock your hand moves the maximum amount no matter how slowly you turn your head. (First person perspective)

To recreate if you dont understand

-Open Bedrock in first person mode

-Open Java in first person mode

-Move your head very slowly in Bedrock and take note of how much your hand moves

-Now do the same in Java and notice how little the movements are

-Now in Bedrock move your head relatively fast and take note of the amount your hand moves

-Now do the same in Java and you will notice it is about the same

Therefore Java is scaled whereas Bedrock has a set amount of how far the hand moves