I agree lock and prop are the same. But second row is a bit different , just marty can play all three . I don't think he is suited to second row middle prop for meStrange, I've been reading here all week that there is no difference between backrowers and props, it's just a question of if they are middle players or edge players. Lussick has played plenty of minutes as a backrower, which in my opinion is his best position.
I guess it's whether it suits your argument or not, because Tapau is a prop, a lock and now a backrower, but in his case there is no difference.