nable, arbitrary, or fanciful." Bluestein v. Cent. Wis. Anesthesiology, S.C., 769 F.3d 944, 957 (7th Cir. 2014); accord Am. Copper & Brass, Inc. v. Lake City Indus. Prods., Inc., 757 F.3d 540, 543 (6th Cir. 2014) (characterizing review of a class certification decision as "very ["84] limited"). Of course, defe