That is to say... if the goal is diversity, which is a good goal, you should probably split some of these larger countries up. Especially countries like India which are not dominated by any one ethnic group. There is no equivalent to the Han Chinese in India.
Unfortunately, the basic precept here seems to be 'has brown skin' makes you exactly the same as anyone else with brown skin, which leads to absurdities, such as California's old anti-miscegenation law that considered Indians and Mexicans the same race.
Mauryans were an empire which means that they ruled over disparate nations
No the country of India is in fact not at all united. The various jatis worship different gods, speak different languages, have distinct cultures. Just because they all celebrate a few holidays in common and have some shared cultural beliefs does not make them the same
This is like saying every Roman Catholic is an Italian.
Lastly, the Mauryans never ruled all the way to South India. This is the first time in history the entirety of 'Bharat' has been under one polity (although arguably with the exclusion of Pakistan and Bangladesh, even this is wrong).
Since when does a country mean a single cultural group? By that metric Switzerland, Russia, the UK, Belgium, France, Italy, Spain, Central Asia, most of SE Asia, any country in Africa, large parts of the Middle East and South America are not countries. For that matter, all of China isn’t Han Chinese, there are Tibetans, Mongolians, Uyghurs, Zhuang, Hui etc.
The difference is that no one clan in India comprises any majority. Again, imagine a country where the french lived next to the english and the italian (like literal next door neighbors), but kept their own languages, customs, etc and only intermarried people like them. That is India. There is ample evidence for this. The differences between the cultures can be extreme.
It is relatively recently that any person in India would even claim to be 'Indian'. Most identify with the state / jati they belong to. Yes, they're 'Indian' in the same way that an Indian is 'Asian' or an Englishman is 'Eurasian', but it's not a coherent identity.
The indian gov't is certainly trying to make that a reality (this is the source of their 'Hindu nationalism' -- which is really a particular kind of North Indian hegemony), but it's been a long time coming, and there are a lot of issues with it.
There is no quota for the H1B visa.
There is a quota for the number of H1B visa holders who have then additionally been sponsored by their company (something which costs a company $20k at a minimum) that can get permanent residency in a year.