Twice my teams alliance has been paired against the single all defensive alliance, in Waterloo against (68, 830, 758) and at GTR (48, 1006, 379). Both times we were the main offensive robot for our alliance, and both times it came down to ramps.
in Waterloo it was all ramps, 830 played some smart D and beat us up, we could only scored a couple, and we advanced because we had the better ramp bot (thou they didn't move from the home zone).
At GTR 48 was a feared defender... they could shut anyone down, even 1114 was scared to face them (1114 is amazing at scoring through defense). Being the top scorer for our alliance we knew 48 was going to be on us the whole time, and they were. They are smart defenders, not only is their drive a beast and can push anything their drivers are smart 'time wasters'. At the beginning of the matches they would trap us in our home zone, the only way we could get by is kicking it into high gear. Then when we would go to score they would pin us there for a while before or after we put a tube on. These guys are smart defenders, against two good scores they were able to keep us to 4-5 tubes in total (usually separated), and it all came down to ramps (which we fell off
). If 48 hadn't lost their track I believe they would have made the finals and given 1114 a very hard time.
After all that I would agree that a defensive alliance can be very effective, but must have a very good ramp bot to back it up. However, an alliance with two elite scorers is still very tough to beat, even with the best defense.