Oh god, I usually don't like bans but Cresselia is definitely ban-worthy. There's really a HUGE influx of dark types to the point that most teams start falling off with a combination along the lines of Cresselia + Fighting-type. Yeah, I know you're thinking "Cresselia and Fighters are checked by Spiritomb alone!" But Spiritomb cannot beat Cresselia 1 vs 1 unless it runs RestTalk Calm Mind. And those need Dark Pulse because mono-attackers with immunities just doesn't work. What does that mean? Substituting Fighters, or foresight Hitmons, idk, are more than enough to just wreck most Cresselia counters. Now, yes, do remember that there are 4 more teamslots left to support your Cresselia!
Oh, then there's the factor that Psychic + Dark + Fighting cores are not very fun to play with, but I don't think that's a good argument.
Yes, Roar can phaze away Cresselia, but this is only a temporary measure. Cresselia will pop right back, wall an attacker and proceed to set up yet again. However, it's not completely the end of the world for Cresselia. I agree that there are multiple non-Dark checks and counters to SubCM Cresselia as a sweeper: Munchlax, Quagsire, Mandibuzz, Perish Song Missy, Aggron, bulky Klinklang, Haze Cryogonal, bulky SD Roost Scyther etc. I remember when Cresselia was around, people were coming up with non-Drapion counters more often than not. (Yeah you could say that's only because all Cress teams had a solid Drapion counter but that's besides the point.) Well, I don't really like any of Munch, Quag, and Mandibuzz, but it's not like stall's any viable here now, is it... IMO Cress should be voted + banned, unless people think that's a serious waste of a time. I mean, can we see a more developed meta where not everyone spams CM Spiritomb, and then ban it?