It is not as though DC films has made great villains, only Christopher Nolan has made great villains. Even Scarecrow is more interesting than Malakeith... but after Nolan the DC villains have been mediocre at best.
But it is still a different policy. If Parallax and Zod were weak, it was due to a lack of execution, a lack of ability. In contrast, Malakeith, Red Skull, etc are weak because there is no interest in making them interesting. Marvel's writers might be perfectly capable of producing great villains, but they are choosing not to. In fact, Whedon himself has helped create many villains more interesting than what we are seeing, like the reavers and wolfram and hart.