Hmm, not so sure about that. In my opinion, Anna is definitely not as big of a star (especially in terms of name recognition) as Halle Berry. Beyond
Cloud Atlas, Halle's been fairly quiet in the theaters and yet somehow she is still dominating the media and award shows circuits constantly. In addition, Halle has always been in the top billed 4 actors in the trilogy (and received 2nd billing in X3), so I have a hard time believing that this franchise's biggest female star wouldn't get the prestige credit in favor of a less popular actress. They both have Oscars however, so I guess it could be a toss-up but I doubt it.
I'm more leaning to this photo placement demonstrates the characters' relevance to the story...which deeply bothers me because once again Logan is on top and is followed by Mystique which is just...weird.

But that's studio politics for ya I guess. I realize that they aren't following the DoFP comics to the letter but if they were, Storm and Kitty would be way closer to Logan on this list. But the fact they are on the top row shows they will have bigger roles in the overall cast.
EDIT: Just checked and realized that Anna had the "and" credit in both of Bryan's past X-films. So who knows...