Let’s say again that you wanted to go from doing 120 to doing 133, and you were going to do this by adding paragon and adding a multiplier.
To go up 13 GRs you need to do 1.17^13 = 7.7x damage.
Getting to 5k Paragon gives you a 1.5x multiplier.
7.7 / 1.5 = 5.13, i.e. you’d need about a 5x multiplier (+400% damage).