in aircraft movements, yes.
and because of the pulldown of ATL as a hub for FL, yes. WN will not push as many passengers thru ATL as FL did.
But the increase in the size of aircraft is being driven by DL's reduction in regional aircraft; ironically the 717s that FL is eliminating and which are helping drive up WN/FL's average aircraft size is also helping drive up DL's average aircraft size as well. Same aircraft, different operator and users and both achieve the same goals.
And as UA and AA both add more large RJs and retire small RJs, their average aircraft size will go up as well.
AA and UA are indeed fighting it out for the Chicago market along with a presence of several low fare carriers.
Given that MDW is closed to being maxed out, ORD's ability to grow will fuel the growth in air travel for the region.
Still, ORD is quite a way from becoming on par with ATL in terms of passengers.