It doesn't seem that long ago that the Diamondbacks had a dangerous offense. Sure, there was tremendous strikeout potential, but with that also came power and runs. Even if no one guy was mashing 40 or 50 home runs, nearly every regular player seeming was hitting 15 or 20. If they did anything wrong it wasn't striking out, it was playing on teams that had tremendously awful or inconsistent pitching.
So changes were made and the Diamondbacks we used to know went away. There's nothing wrong with change, and there's more than one way to construct a winning team. The dampened offense is only noticeable during losing streaks, when it seems like getting any runs will be an impossible task.
If you look at most of the traditional stats, then the Diamondbacks are just average (even considering the bad couple weeks they've had). Batting average and OPS are just below NL average, and home runs are just above. BABIP is at .300, so it's probably safe to assume that they're not exceptionally unlikely (or even worse, lucky and still terrible).
The more advanced stats tell a different story, and it doesn't look pretty. The weighted on-base average (wOBA) is still about average at .310. In other words, the average offensive output of the Diamondbacks is truly average. When you look at weighted runs created plus (wRC+), which attempts to express how many runs are created by the offensive output and is based on wOBA, the floor falls out. The Diamondbacks have a wRC+ of 87, which is 8th worst in MLB. wRC+ was created to try to have an index with 100 as average, so the Diamondbacks fall well below that.
Using 100 as the average for team production is problematic (because teams are generally composed of both studs and jokers), so we need to look at who exactly sinking the offense on the D-backs. The usual suspects are there, and some surprises. There are three players with over 100 PA and 60 wRC+ on the Diamondbacks: Willie Bloomquist, Paul Goldschmidt, and AJ Pollack. Justin Upton isn't much better, currently sitting at a 81.
There are some bright spots, however, at the top. Chris Young and Cody Ransom both can't expect to continue to post wRC+'s over 160 (both have only about 50 PA). Lyle Overbay has been very good in limited time, getting a 139 in 58 PA, but he's another that probably will decline as he gets more time at the plate. No, the big, consistent contributor has been Jason Kubel.
Kubel has put up a wRC+ of 130, and he's not hiding behind limited time or platooning. Imagine how bad this team would be without him.
Of course, things should get better when Young and Drew get back, replacing Pollack and Bloomquist, but the rest of the team needs to get it going if we're to feel confident for the end result.