Strawbyx posted a pvp video of their TR in the class forums, and what do you know our favorite Black Hearts members Catwoman and Starkiller can be seen! Looks like it was a onesided match. ;) https://www.youtube.com/watch?v=9Ojdd13XAKw
well i'm going to guess your defense goes against the enemies power/armor pen, which could very well negate the effectivness of those stats. deflection has no such check against it.
GWF get 50% deflection severity. Also from what i've seen CON does not give damage resistance for GWF just resistance ignored and HP. DEX give AoE resistance.
i also think a dex build lends itself to life steal, as con does to regen. less hp+high deflect+high crit and lifesteal=an easy way to keep your hp up fighting the hordes of mobs you'll be facing. although, i haven't seen any tier set GWF gear with much lifesteal on it.
if you aren't a rogue it does benefit you to have another attacking companion so you can set him up to flank so you get constant combat advantage. you pretty much should always be attacking under combat advantage.