So after getting to level 27 I've got to say the lack of explanation is getting to me...
Example:
Roland's Deploy skill gives +20% "cooldown reduction" on his turret for every point spent in it. At 0/5 Deploy, it seems like the cooldown doesn't even start until the turrent has despawned, at which point it takes 100 seconds to cooldown (as listed on the turret skill). At 5/5 Deploy (i.e. "Cooldown reduction: +100%"), the cooldown starts immediately after the turret has deployed, and it takes exactly 60 seconds to cooldown. However, I have a class mod that gives +2 Deploy, and with it equiped it takes 50 seconds to cooldown (with 5/5 Deploy, essentially giving me 7/5 Deploy).
HOW DOES THIS MAKE ANY MATHEMATICAL SENSE?
P.S.: The only way I can make sense of this is if the standard "cooldown reduction" once you put a point into Deploy is 20 seconds. That way "cooldown reduction: +100%" means 40 seconds of "cooldown reduction," (100% of 20 is 20, and 20+20=40) and if I get +2 more to Deploy (i.e. 20% more cooldown reduction), I get "cooldown reduction +140%," (140% of 20 is 28, and 20+28=48~50...)
This game needs to come with a guide! And paying $20 for a Prima Guide is not what I mean; it needs to be included in-box...