Skill... It should be fair towards new players aswell like it shouldn't require a donator to kill another donator.
Try as a 2GA soldier to go against a nailgunner with an MP5, it wont happen.
Currently it requires someone with an orsis or an MP5 to take down someone with for example nailgunner or RPG as they most likely also have a few donor guns which leaves new players at a HUGE disadvantage.
Conclusion: People shouldn't be required donate just to even out the ods.