It would be good idea to change some skills into passive ones. Every character would get one slot for passive skill. Why this change? Because some skills can enhance the gameplay, but are not worthy to be included into 3 skills and are almost never used.

My suggestions:
Devices - Mastery
Survival - Knife technique
Explosion - Charge compression

Maybe even add Wind shadow as passive skill, while this skill is often used, it would add variability into camuflaged builds.