Since Minecraft 1.9, projectiles have done about 2 blocks of knockback to players and most mobs.
Since release 1.14, this is no longer the case. While projectiles still do 2 blocks of knockback to most mobs, they now do only do about 1 block of knockback to players.

behavior in 1.9-1.13.2

https://youtu.be/53zLhlcXcjg 

behavior in 1.14+

https://youtu.be/PRaEt-RwsEo

Comparison of behavior between players and mobs now 

2023-11-25 13-47-53.mp4