The zone starts and competition quality has declined for Nurse, who has seen a 2-3% increase in o-zone starts and has played less with McDavid's line since Ekholm arrived (which means less against other top lines usually).
Though he still plays the toughest overall minutes on the Oilers, Ekholm-Bouchard has taken the cherry offensive roles as they've promoted and contributed offensively at a level that no Oilers defense pairing has since 08-09.
Essentially playing less with McDavid's group has meant they're playing a grittier game against grittier players and with better checkers like Bjugstad and Janmark. That suits Ceci a lot more.