Cartels shouldn't have to generate extra money over the processing cuts taken. If you own a cartel, you have the advantage of no cut while processing, take advantage of that when you can. Honestly, the 2 best cartels to own are Wongs and Oil. They probably bring in the most money. Arms & Drug are more "for the fight" cartels.
As for the stats, i'd like to see a cartel section on the stats page that shows what each cartel generated per day and lengths of ownership. i think that'd be interesting. What they don't need is individual stats like "time in cap" just so those Boomer gang leaders can figure out gang paychecks...