If I remember correctly, integrating Siemens Profibus Master network on Step 7 could be done from v5.4 and later. Before that, the only option to add a SIMATIC PC was NCM Manager. However, you both are right, one would not find any interface difference between the two software. I mostly used SIMATIC MANAGER (Step 7) to configure Profibus communication on the robot (Master network) and Siemens PLC (Slave configuration).
Nowadays, I use TIA Portal (for new S7-1200 and S7-1500 CPUs) and WorkVisual for KRC4 robots.