While alot of them get steamrolled, I do run into 2 group types frequently:
1. Newbies - they don't play their class well because they are still learning the game
2. Bad players - not newbies. They don't have a leaf, often have bad/empty gear slots and still play at a newbie level.


Both of these groups would totally fail if normal dungeons got harder. But all of group2 would always queue for the harder dungeons because of better exp.