Again you are conflating jati and varna and no they are not trivial semantic nuances. These divisions persisted everywhere in far more rigid fashion - Western Europe, Japan, Russia, Korea......

Look for my earlier comment in this thread. When the British codified jati+varna into Caste they acknowledge that there was mobility at the bottom though not at the top. The Census of Indian in the 90s acknowledged the same thing. This is not and never has been as rigid as you think.