You should receive overclocks for the class you promote when you get a promotion

I've promoted my driller 3 times, and each time I get assorted junk for classes I don't play; I would feel a lot more purpose in promoting if I at least got random junk for the class I do play.

Update: I've took everyone's advice and have been enjoying all the different classes. I have a ton of overclocks for a bunch of different gunner's guns and have been trying to unlock all of them to use those and it's been pretty fun. I think my main complaint still stands that I didn't have that many overclocks for driller, so maybe the first few promotions on a character could give you garunteed matrix cores for that character to get you started, and then have it be random after that to encourage you to branch out