Even if that were the case... The game is very punishing for anyone besides a tank to take damage. If your mage starts getting attacked it doesn't matter what armor he wears... he is going to have a bad time.
I'm going to laugh when everyone running around with naked ranged characters get whooped by enemies burrowing, charging, and teleporting past their frontline.
For example, say your mage/rogue/whatever has ~75 health. The mobs in this game hit hard. Having a DR of 6/8/10 compared to 12 isn't going to do anything to keep you alive. You are far better off just doing as much damage as possible.
Actually wouldn't that 6/8/12 be half as good as the 12 and twice as good as 0? And wouldn't the penalty also be less than it is at 12 and more than it is at 0?
Oh wait I forgot this is the internet so everything has to either be either awesome or useless with no middle ground anywhere - sorry my bad...
It's not that there is no middle ground. It's that the middle ground is useless.
When you get struck reliably for 40 damage, it's not going to matter whether you have 6 or 12 DR.
What is going to matter is whether you can kill the thing before it kills you or not, or at least do enough damage to it so your next team-mate up for the grinder doesn't die. Or the tank, for that matter.
There it is again - awesome or useless - I've been playing the BB on hard for a lot of hours with a lot of different PCs + BB team + adventurer teams and have outfitted all of them in various forms of mostly medium armors (no naked adventuring and virtually no plate either) and I rarely have party wipes and while I might lose a team member or two in battle we win much more often than lose. I have also avoided almost all enchanting because I am more interested in what the basic weapons & armors are going to do and these partyies have for the most part done just fine. So I'm sorry but I just am not seeing the whole "useless" thing.
And there it is again - I do X and I'm not instantly murderwiped so everything is clearly balanced.
Like I said earlier, you can make it through the game any way you want. It doesn't mean that it's well-balanced or that there's good incentives for you to use X over Y. There is, again, no accounting for taste. But if that is the best argument you can come up with, I think that pretty much just highlights the issue for everyone else.
As has been explained in detail, there is no reason to use the middle-ground. If you still do it, well great for you, huzzah, but let's not pretend that you did it due to any reasonable level of cognitive thought on your part. Let's not pretend that you did it because it's a good choice or that it makes sense.
Most of us would prefer the game to have a semblance of balance and for our choices to matter, or be able to make choices in style without knowingly gimping ourselves or shooting ourselves in the foot. As of right now, anyone that knows the mechanics of the game lives with the knowledge that unless they go by this false choice, unless they go by this armour dichotomy, they'll be actively working against their character and the party. They will be playing at whatever difficulty +1.
Now, many of us can live with this knowledge. Again, just because I see a flaw in the game and point at it, doesn't mean that I'll be min/maxing like some diehard tryhard come release. I have a very specific character in mind, and it's going to happen, whether this is fixed or not. But this doesn't have to be this way. It could be better and it should be better. A bad game mechanic or unbalanced content doesn't suddenly become good just because the computer's harddrive doesn't catch fire and the monitor explode the second you boot the game up.
In a nutshell, if you do not adhere to the armour dichotomy as present in the game and you still succeed, and if you still do well, you are doing well in spite of your choices. Not because of them. To me that's like drinking the poison potions in D:OS and say that they're really good potions - no, just as good potions as all the others -, as evidenced by the fact that I still haven't wiped.