Given you want to improve at all and you notice that the lowest dungeons to run (MC and TR) take really, really long, I assume that you would stop and start to think at one point, about how you can improve your gameplay.
If you do, then you will start to look for information and get a grasp of what to do with your class, which includes looking for the correct rolls.
If you don't, then you will still be an exceptionally bad player by the time you can queue for FLNM.
How do you expect people to learn their class in MC and TR? Have you used MC and TR through IM? Because that is the only way average/casual, new player can get a party, no one in LFG is going to accept DPS in legendary gear +1 or with 1 or 2 purple pieces, because everyone wants fast, clean runs. Let's say player wants to improve his gameplay, looked up right rotation and ques MC, the chance to get a tank and be able at least try to do his proper rotation is very low. Most likely, he will get another 2 dps and they will die in order of who gets aggro, rez and die, rez and die until boss dies. Range runs from boss and dies, melee runs after boss more than attacks and when ranges dies, boss turns around and kills the melee. I can't see anyone enjoying game that way, let alone stick around long enough to get to 516 and then even attempt to have right/good rolls.