The thing with frak, much like "frell" on Farscape, is a way of being able to say fuck without getting censored. And, as others have noted, a homage to the original.

So yeah, I won't disagree that it's an insanely dumb word and I wish people could say fuck on TV without getting all up in a tizzy about it, but that's really the purpose of inventing silly words such as those. It's also a nice "screw you!" to censors because it's so obvious what the word means but because it doesn't have the same letters and pronunciation, it's okay, which basically pokes fun at the ratings system.