Like I said - I'm not an expert in 4e builds! I only worked out I was wrong about this when I got home and looked up my PHB3.Your 2nd character is equipped with Hide, which a hybrid SM/Barb is not proficient in (SM is leather only). Changing back to Drowmesh is -1 AC, -1F, +1R.
Compare your new build to a swordmage wielding a two-handed weapon, and taking hafted defence (which would be -1 AC, +1 Ref compared to your current build):
AC: +1 for hide armour vs leather, -1 for changed class features (+2 barb agility vs +3 from warding & 2 warding feats), > overall no change
Fort: +1 for masterwork hide, +1 for hyb barb, > total +2
Ref: -1 for losing masterwork leather, +2 for barb agil, > total +1
Will: -1 for hyb sm rather than pure sm
Unsurprisingly, the shift to barbarian and hide armour ups Fort defence. The "surprising" factor here is Barbarian Armoured Agility - the +2 Ref turns out to work pretty well when you hybrid into a class that has Int or Dex as a primary stat. So instead of a hit to Reflex for switching from leather to hide, you're getting a boost.
Anyway, thanks for posting about this build - it works for an old RM character that I've been thinking about trying to rebuild in 4e.