As printed, GWF adds +1.33 damage on 2d6, +0.83 damage on 1d12, and +0.8 damage on 1d10.
With your change, GWF adds +1 damage on 2d6, +0.75 damage on 1d12, and +0.7 damage on 1d10.
If you change it to "turn any below-average roll into the average roll", it adds +1 damage on 2d6, +1.25 damage...