I'm going to bet once PoE is out you'll wonder why no other devs do this and prefer it to the current situation in future games.
Sure, if I realise that always avoiding combat whenever possible is fun. Which will never happen.
No, and No.
You've fundamentally misunderstood how the mechanics of D:OS work if you think this.
The reason is simple: there is no NPC magical immunity. You can, if you want, complete all quests then massacre the entire inhabitants of cities (something I did in Beta to prove a point about the non-functioning criminal code). That achievement for killing Arhu is there for a reason.
To put this more succinctly - Quest Reward flags [Xp, Items et al] and Kill flags [direct XP] are not really entwined in a meaningful way. Look at the code if you want to know why.
Killing all of the world's inhabitants for probably less than 2% of all XP in the world is game breaking because it makes your party too powerful?
*facepalm*
Anyway, yes, we already covered the xp double-dipping problematic (which really isn't a serious problem). There are many ways to fix this if the designer is competent and not lazy. This ridiculous argument is getting really old really quick.
As is your entire post.
