Caste is not a British construct. They did not understand it properly but all evidence suggests that they in fact encouraged caste fluidity in most cases. The mapping of castes existed well before British. In fact you can look at smaller colonies such as Goa which were never under British rule and you find very strong existence of caste. Same with hindu society that moved to other countries. Even if it was a British construct it is still the failure of Indian society to continue with it if you assume it is bad.
> Varna is occupation and jati is tribe.
This is not true. There is no basis for Varna being treated as occupation. Gita and all other books are very clear that this is a qualitative classification of people where birth also played a good role.
In modern sense your definition of Varna is worthless too because people in same occupation show no solidarity along these lines. But show strong solidarity along the "jati" line.
> Jati is tribe.
Jati is inherited from father. In that sense it can be seen as a tribe. But it is also a classification very similar to Varna. Tamil Brahmins have completely different gene line from say Chitpavanas and yet both are seen as Brahmins and they will quickly form a good relationship compared to say a Chitpavana and Koli (fisherman).
Calling Jati a tribe does not explain this.
The broad idea of "caste" is probably a better term as it seems to represent really well the underlying social effect everyone is more interested in.
-- Untouchability was present in some cases, but it was between 2 jatis. Meaning, one jati would consider the other jati as untouchable. However, it was not between varnas.
This system became more rigid after British started classifying people into different castes, providing benefits to some and taking away some from others, and that's how the caste system evolved into what it was. --
Most of the literature around "caste atrocities" is completely bogus and made up and does not stand close scrutiny. People might have been treated as untouchables, but it was not very different from you not willing to touch a homeless man on street of SF. Now you might find that there is very good mapping of race and homelessness but it is not the race which makes the person untouchable, it is the filthy lifestyle.
Most of the "low caste" people in India actually had very low social capital, were less civilized and had poor work ethic. Some of those castes quickly improved and suddenly became "upper caste". For example the most revered King from India is Shivaji who was from a lower class of land tillers who along with his entire tribe became one of the greatest ever "Kshatriya" (higher caste) person ever.
Once a person or tribe builds social capital they automatically transition into upper-caste. Those who do not, remain at the bottom.