So for the past three days now I've been playing more roles outside of which I'd typically play, mainly being a SO. And from that experience I've seen how little Marines do objectives which contribute to lowering the Defcon level. I've also seen rounds in which Marines do go after objectives which usually lead to things going to Defcon 4. But I've noticed that this usually occurs only mid to late game, and even with the Marines on their A game the lowest I have ever seen it go was 4. What I'm saying is the current objectives are unbalanced, and yield to little to contribute getting past Defcon 4. I also heard that collecting fallen Marines can help lower it but I personally don't see this happening mainly because Marines don't have the time to recover bodys which put them out of combat for a long while.
The first suggestion I have is to rework the scrap notes and other random items you find as I feel they don't add enough to the level.
I also don't see nor expect any Marines to drag bodys back across the map back to the Alamo as it's simply (at least in my opinion) not fun and is very time consuming. And because of this I think penalty's from this should be reduced or entirely scraped in favor of collecting Dog tags.