United WBs:
227
Delta WBs:
174

When considering this difference, it's important to realize UA does 1 Capt/3 F/O 4-pilot while DL does 2 Capt/2 F/O. I don't know how many WB Captains UA has, but the effect is pretty clear comparing Captains/airframe at DL. On the 767-400 where it's pretty much all 3-pilot augmented, we have 9.4 Captains per aircraft. On the 330/350 where there's varying degrees of 4-pilot, we have 12.3 Captains per aircraft. 330/350 are also growing fleets, so I'd expect them to be understaffed.

If the reason to compare is thinking about how much opportunity there is to be a WB Captain someday, they are about the same number.