It is possible to undergear mechanics-based content in TOR. It's practically impossible to underskill that same content.
I will agree that it is impossible for a underskilled group, but many underskilled players are pulled through content.
The groupsí skill base is more important than individual players in end game content. Anyone that thinks NIM EC or HM TfB is a breeze; need to take a moment before their next operation to thank their entire group because you are an extremely lucky person to get with such great players. You may be just as good as or even better than any of them, but you are not going to carry average players through that content and still think it is easy. I know, I play with two very good groups and the difference between healing them and other groups is extreme. Players that know the mechanics know their class, their role, the rotation and enough about the other classes to know your capabilities makes the game both fun and at times extremely easy to play. Do the same content with 7 random pugs and you will quickly figure out you are not as great as you think you are.