Their point is that if you go into a duty post 30-35 on a base class, and everyone else are on jobs, then they are carrying you because your base stats are low, and your skills are super limited. This isnt something you can control by choice either, they will have to work harder to compensate the discrepency between the dungeon tuning and you.

The base class challenge only works as a challenge if you are all on base classes, because you all work harder, so its distributed. What youre doing is no different to going into a level 50 extreme unsynced with a level 70 companion. You havent duo'd it at level 50, they have solo'd it for you.