Hi, it's me again, glad to see my mail in the list. I found an error in my theory finally, so this is the fix. On that mobs you can increase reputation only until u got friendly with certain part of Cartel. After that this faction rep will no longer be increasing, while 3 others will continue to increase(until friendly too). So after you have reached friendly with the whole Cartel, only then it's worth to do quest run in Dire Maul.