deleteme123456
Explorer
Without the +3 bump (+2 more than light) to AC in heavy at +4 and +6 you'd fall behind light armor because the light armor is getting +1 at level 8, +1 at level 14, +1 at level 21, and +1 at level 28 assuming an even to start. So if the heavy armor only got +1 like light, then light armor would be strictly better for anyone who could afford the int/dex, and many defenders would feel like they had to invest in those to keep their AC up.
As-is, if you assume that you get +4 armor at level 16, then that extra +2 catches heavy up to the light guy who had gotten +2 by then from stats. At level 26 if you get +6 armor, then that +2 can pass the light guy up for a brief moment until level 28 when the light guy catches back up.
As-is, if you assume that you get +4 armor at level 16, then that extra +2 catches heavy up to the light guy who had gotten +2 by then from stats. At level 26 if you get +6 armor, then that +2 can pass the light guy up for a brief moment until level 28 when the light guy catches back up.