Inability to get a yard when you really need it is a hallmark of the West Coast Offense and the Zone Blocking Scheme. The former doesn't typically commit to the run, and will more likely rely on a quick pass - it has been a hallmark of the Andy Reid offenses, which Harbs is most familiar with. I'm generally a fan of zone blocking in the right scheme, but it is a very reactive, east-west approach: O-lineman steps in a direction, and doesn't really know who he is going to block until the defense slants, bulls, or stunts.
Our offense is a hybrid of West Coast and Zone Blocking. That yard will continue to be hard to come by. That's why we need a bigger center. When in doubt, QB sneak and pray.
I think the problem is that we don't have the players to actually run a West Coast offense. The West Coast relies on accurate, timed passes, quick hitters that can supplement the run game. You also need a bit of a mobile, meaning more agile, QB that can move around in the pocket a bit to extend a play. This is why guys like Alex Smith can actually put up decent numbers and win you games even though he's not known for having a cannon arm. Joe Flacco doesn't have great timing, doesn't have great touch, and isn't exactly agile. Secondly, it relies heavily on Tight Ends. Since it does your TE's need to be playmakers. While Pitta is excellent in actually getting open in zone coverage and has very good hands, he's not a playmaker. I think he'd be a good #2 move TE option at this point in his career. Hopefully Maxx Williams is the guy we think he is. Because the short pass replaces your run, your TE's can get away with not being the best run blockers in the world. Third, your receivers don't have to be fast. They don't have to be huge. They need to have good hands and do something NONE of the Ravens WR can do, and that is get separation. We run HORRIBLE routes. How can you run a spread formation with no backs and get nobody open? Yes, this actually happened several times last season. Lastly, you need an O-line that can pass protect. Most of our line is not good at that. They are plow ahead maulers and not guys that back pedal well. Ditch the zone run/west coast garbage. We do not have the right talent to run it. Go power run, twin TE, playaction. This is the single most important thing the Ravens can do to win next season and it won't cost them a single penny to do it.
Football is a simple game, you block, you tackle, don't make it complicated, it's not.