in the PS3 vs PS4 video, the Look Back test isn't predominantly showing input lag, it's showing the delay timer... Look Back isn't Press R3. Look Back is Hold R3... if you fully press R3 in, fully, but instantly let it go, you don't Look Back. You have to Hold R3, so the 'delay' isn't input lag but the Hold delay.
also, most of the videos start from a neutral button position so they're not showing just input lag or input reaction time... in GTA V, pressing R2 is not actually Shoot... it's Aim. Half-Press R2 is Aim, Shoot is Full-Press R2. Also, R2 has a small deadzone, and obviously L3 or R3 have significant deadzones. so when you quickly fully press R2, most of that physical movement is not actually Shoot... it's a deadzone or Aim. You're not even pressing Shoot until the button is over half-pressed.
I think the far bigger problem than any input delay that hurts free aiming are the stick deadzones and aiming acceleration being rather sudden and fast once you get past the large deadzone... which is why aiming in GTA V can be rather jerky, the large input 'free' zones (which is not input lag) can can lead to a lot of initial over-compensation or under-compensation