Ooops. Misread brutal.
Maths put brutal 1 1d8 at 39/8, or 2d4, or half a step up. Brutal 2 is 44/8, or 5.5, or 1d10. The balance is better for smaller weapons. Makes taking a brutal 1 weapon worse, but gives swingier damage.
I actually quite like the exploding dice idea actually regardless of...