@HeinzGud you can participate as long as you don't flame-bait. I merged your existing thread since it was pointlessly inflammatory
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Now on topic:
I used to have a different view on this - that Buddhism was "reformist" and "rational" etc. This does not hold up to scrutiny. I feel most of this is came from a very orientalist interpretation of things. Then later folks like Karl Jaspers shoehorned Buddhism into his "Axial Age" theory
Reading actual philosophical texts changed my view.
The main difference between Hinduism and Buddhism is independent origination vs dependent origination. All this extra caste, reform etc is fluff added by politically motivated historians. Hinduism says everything emanates from all pervading Brahman. Buddhism says everything depends on everything else, the nature of reality is shunyata i.e nothingness.
Sure Buddha probably challenged the traditional social order, but the followers of Buddhism were elites. It's a sophisticated philosophy, you can't expect the common folks to understand and appreciate it. Despite imperial patronage Buddhism was probably never a majority religion. The common people of India probably just continued following whatever were following earlier.