So they got a no name to play Viper. At least it will be cheaper to pay her than Jessica Biel.
Having a bunch of names doesn't mean a movie will be any good. Just look at all those Garry Marshall ensemble "romantic comedies." Hell, just look at the last Wolverine movie.
You only need to have "enough" big names to help sell a big movie. In this case, "Wolverine" is really the main selling point. Then Hugh Jackman.