Well, yes, that's a given. However, unlike you, I believe that he's a different player as a central defender. Also, I can tell you several instances where Rojo's defensive errors at left back has caused us many problems, even more than during his stint as a central defender.
The one error as a left that sticks most in my mind is Vardy's first goal against us at the King Power Stadium. Rojo went in too early at Vardy and completely failed to win the ball. He tried to chase back, but Vardy was already past him, and his cross (yes, the ball crossed the line, but that doesn't matter) was met by Ulloa, which put the pressure back on this. Rojo diving in too early gave Leceister a break, and Rojo's mistake allowed Leceister to get the goal back. I also remember several instances as a left back in that match where he'd press on Vardy but Vardy would often beat him.
As a central defender, though, the only times I remember him causing us problems are his sloppiness on the ball, him flustering under pressure, and him losing aerial battles. I've rarely, if ever, seen him overcommit and leave a gaping hole at our back line. I've rarely seen him make mistakes that he'd make as a left back.