Yes, SS/CF/C are the hardest positions to play. Because only a fraction of MLB players can capably play those positions defensively, the offensive threshold for being viable at those positions is lower. 1B/LF/RF are the easiest positions to play, so the offensive threshold for being viable at those positions is higher.
Tim Anderson's offensive numbers make him an All-Star shortstop, but if the only position he could play was 1B, his offense would be nothing special.