Football Outsiders publishes a "points per drive" Stat that I think you might like. That's probably a better measurement for your purposes, since if you have a ball-control offense and a bad defense, then you'd get an inflated result if you have +5 mins time of possession every game or something.
I think that yards per play is a measuring stick that you might like, as well.
For me, it's hard to say that this year's offense is going to be worse than last year's. Even if Kolb starts, he has another year in the system. If Ryan Williams can stay healthy, we have an explosive runner teams have to account for. We've added weapons in the passing game like Floyd and Rob Housler (who I don't really count because it takes some time for rookie TEs to adjust to the NFL). Skelton, if he starts, has the attention that a 1B QB gets from the coaching staff, as well as his first real offseason.
There are a lot of reasons to think that even with the issue on the offensive line, this offense could at least grow into mediocrity.