Aside from the 737-500s (which are a small set of the fleet and only have 8F), most of the CO fleet compares quite well to the DL fleet. The 737-700s both have 12F, the 737-800s have between 16-20F domestically (the Guam-based ones still only have 14F), and the 737-900s have 20F.

The thing where CO lacks is the lack of a 757-200 Domestic, as all of their 757-200s are in an international configuration - that being said, they're using occasionally on domestic routes - not much to make/break the system. The 757-300s both have 24F.

The biggest difference with CO is that (a) it's reasonably-priced F so people will pay for it and (b) the ease of elite upgrades from higher fares that clear straight into F. A Platinum needs to book a M fare and will clear into F immediately at the time of ticketing (Golds I think can do this on a B fare). There are a good number of Plats out there that will buy the M fare and take the confirmed upgrade immediately at the time of purchase.

The other big thing that hurts CO with upgrades is their (over)reliance on ERJ-145s/CRJs, which can tend to push elites onto a mainline flight rather than deal with RJs. Add in CoEx facilities at IAH/EWR are bleh-ish (B84 at IAH is one of the worst RJ experiences out there right now), and people do make a concerted effort to avoid those flights.