Instakill Boulder Nerf

My personal idea is to make the boulder 80-100 rock and lowers momentum significantly while holding it. Also, make able to block arrows and slashes when you're holding it; but prevents you from doing anything except for moving. They give a 0.5-1 heart damage and knockback thrown a bit beyond point blank, and 1.5 hearts at any further. archer grapple will be significantly weakened when having a boulder, but still possibly enough to do 3 hearts of damage but no more. Boulders launched by catas, on the other hand, should be mass destruction weapons and should be able to either:
penetrate 4-5 layers of wood launched at full strenth and 1 layer of traps/bridges
3 layers of stone and 1 layer of whatever
instakill all characters when launched by cata
ideas?
maybe reduce boulder hitbox when launched by cata to do less obliteration?