Last season, I lost only two games with my dark elves. Of course, one was the league championship, but we're not bitter.
Under the old rules, I played without a witch elf. My league was bash heavy and so I thought the AV7 and old Frenzy were too much of a liability in that place. But I've bought one now and am trying to develop her. Block with frenzy makes a world of difference (as does having 5 rerolls).
IMO, raw speed, ala Wood elves and Skaven, is overrated. MV 7 allows you score a two turn TD without GFI, and MV 6 with just one GFI. Get some leap on a few receivers you flood the field with and you'll score every time. But no elves have trouble scoring. HE get catchers, but elves are already great catchers so I'd rather give up the catchers and instead get more blitzers, and now witch elves, and have the ability to pop out the ball on D. Once we have the ball, we're on cruise control.
That's the advantage dark elves have. The ability to carry out selective attrition, and live to tell about it.