I just find being rewarded on easy is pointless. Easy should be for eastereggs, and glitches. Leave skulls and achievements to normal or higher.
I think every campaign achievement in Halo 4 should be Heroic or harder, and some only able to be done on Legendary (like in Halo Anniversary). Achievements should be something to be achieved with effort, not easily done.
I totally agree with you both. I think all campaign achievements should be awarded on at least normal or higher. Easy requires no effort to do anything with. I hope 343 takes this into consideration.