You are correct about the problems being mostly due to the OLine. However, I think waiting for the OL to "get in sync" is wishful thinking. The bottom line is the OLine just isn't very good. They were a weak link last year, too, and Elway did little to nothing to upgrade the position. Evan Mathis, who is good (though not as good as he used to be) kind of fell in Denver's lap right before the season started. Until that point, Elway had brought in a few rejects after losing Orlando Franklin, who was probably their best player last year after he moved back to guard. Losing Clady clearly hurts, too.
In some ways, given the lack of a running game and the pressure he's faced, it's remarkable Manning has played as well as he has. Still, though, the Oline's issues are why they haven't been able to run the ball and why teams are blitzing regularly. This will continue, and since Manning can't throw deep to mitigate this, I suspect the offense will continue to struggle all year. Teams can play tight coverage and stack the box, and the Broncos don't seem capable of consistently beating such defense.
Denver's defense, though, and their kicker will keep them in most, if not all, games.