Assault is the class I play the most. Why? One reason only: the spawn beacon.
As others have pointed out, Engineer, Support, and Recon have substantial advantages in their own classes. I do struggle to see any extraordinary value in the caffeine pen. Plus I never use the sling option. (And having extra mags is moot when I die sooner than the need arises to use them... 😄)
Granted: perhaps the ladder is underused — but how often do the maps lend themselves to use them?
So in summary: Assault needs another one or two game-changing perks to make it level with other classes.