"Race" is not a thing in India. It neither exists in history, nor in common parlance. If you go to a rural Indian guy and ask him what his race is, he will ask you what "race" means or if you are referring to a horse race lol.
I would agree that in terms of impact to people, casteism or racism really makes no difference in how people suffer. But to say that the caste system was built on racial supremacy is outright wrong.
The caste system was a social hierarchy based on vocation that was developed 1000s of years ago. So there were Brahmins - who were priests and teachers, Kshatriyas - the rulers and the warriors, Vaishyas - the tradesmen, merchants and land owners, the Shudras - the servants, and the Dalits - untouchables who did dirty jobs like cleaning the streets, toilets, etc., Over the years thousands of castes developed.
In the past there was substantial caste violence, but today it is extremely reduced to the extent that we mostly don't even hear about it.
When it does happen it is usually political or retaliatory (like a guy from one village beats up a guy in another village during an altercation, so they go back and bring their own gang to the fight). For example, when I was in college one of my classmates belonged to a lower caste called "Vanniyar". We did not know he belonged to that caste, because in India you do not ask a person for their caste as a matter of social etiquette and rules. The only reason we knew he was a Vanniyar dude, was because Vanniyars have formed a political party called PMK. One of my other classmates talked trash about this political party, and this other guy got so pissed off for it. This is an example of a political reason due to which you could have caste violence.
Or it is more to do with tribalism - and on this one, sometimes lower castes discriminate against higher castes too. Particularly in government jobs. Because of affirmative action a lot of the government jobs are filled with people from lower castes. If a Brahmin were to apply there may be cases where they will not give him an offer, and instead recruit one of their own. Similarly, even if two castes are at the same "status", there are cases where they choose to self segregate. In almost all of these cases, the people involved are primarily rural or uneducated. If you consider contemporary India, no one gives a fuck about caste barring a few outliers.
Similarly Hindu Nationalism, regards everyone as Hindu, regardless of their actual religion. They consider Hinduism to not be a religion but a way of life. And that people of India, follow the "Hindu" way of life. That is why groups like RSS have Christian and Muslim wings. I don't agree with that, because ultimately it forces a certain "culture" on people, but again it has absolutely nothing to do with racial supremacy.
This does not mean Indians cannot be racist. They most certainly can. But caste and Hindu Nationalism are not racial supremacist ideals. So you comparing them to Nazi ideals is comparing apples to oranges.
Subhas Chandra Bose therefore, joined the Nazis because he fought the British, to free India from the colonial power. Therefore he is a national hero and a freedom fighter. Not a Nazi.