Well, there are only 4 classes and 3 body types to choose from, so you've got to expect one combination to come out on top.
Bodytype is clear because everybody wants to be a free runner (which is obviously emphasized by the game). From there it only makes sense to choose Op since being small means unable to take as much damage (I'm offended by that) and you lose out on firepower.
Soldiers want to be able to take more damage for being frontliners, medics for sticking their necks out there, and engineers while building things, so people are going to be hesitant of trying lightweights in those classes.
It will change once people get the free running urge out of their system.
If I get this, I plan on using all my creation slots at some point for a wide variety of types (probably on both sides of the conflict as well). In my years of gaming I've played every role there is and while I love sniper rifles, knives, pistols, and being sneaky, I'm also the kind of guy that will sacrifice myself for the win, so I'll probably run with a medic first.