Yes, there were atrocities, but it also brought education and modern civilization to India. God has judged those who committed atrocities, as well as those who brought good. If India wants to do back to what it was before, they are welcome to do so.
India already had education before British rule started in 1757 with schools etc. dating back millenia. India had an extensive, decentralized system of indigenous education through gurukuls, temples, and madrassas. Some historical estimates suggest high localized literacy rates before British dominance began to dismantle these traditional system (Refer to William Dalrymple’s “The Golden road”). The British system, notably influenced by Macaulay’s 1835 Minute, aimed to create a class of Indians “English in taste, in opinions, in morals, and in intellect” to serve as low-level bureaucrats.
It didn’t have universal education (but then neither did the UK in 1757).
“modern civilization” - yes and no - India is home to one of the world’s oldest urban civilizations (the Indus Valley Civilization) and had sophisticated legal, scientific, and architectural traditions long before European contact.
The English DID introduce a unified legal system (like the Indian Penal Code) and English-style courts.
Overall English rule was slightly on the positive:
1. it did break the back of Mohammedan rule (note that the English didn’t grab the land from the Mughals so much as grabbing from those who grabbed it from the Mughals)
2. the Indian powers that broke the Mughals (the Marathas, Sikhs etc.) didn’t set up long-term structures
3. the “Sati” etc. were north Indian practices
4. the British did bring modern education, infrastructure and expanded the Mughal bureaucracy while setting up a rule of law
the negatives were:
1. they prevented the Indians from selling to others or buying from others (a captive supplier and market)
2. in their early years - from 1757 to 1800 in Bengal, the Raj grabbed so much wealth from Bengal that it led to famines
Overall for India it was and is a love-hate relationship, like the US relationship with the UK.

This is of a kind of "mythical" proportion - the huge diamond was supposedly the eye of an ancient Hindu idol (never proven, but quite probable) that was taken according to the diary of Alauddin Khalji of the Khalji dynasty of the Delhi Sultanate, he acquired a large diamond when he invaded the kingdoms of southern India at the beginning of the 14th century and looted it from the Kakatiya dynasty. It then passed to different TurkiC dynasties who ruled Delhi before ending up with the Mughals
Then the Iranians invaded the Mughals in the early 1700s and took the diamond. Then the Afghanis (the Durrani empire) got it from the Iranians
Then the Sikh empire took it from the Afghanis :)
Finally the Brits conquered the Sikh empire, then got the orphaned king to come to London where later he gave the diamond to Queen-Empress Victoria
Legally etc. i don't think the Indian government has a leg to stand on for the return
But it has a huge symbolic value for the Indian civilization
you can't turn back time, the British were comparatively benevolent conquerors, but they were conquerors nonetheless who exploited the country for money. the subcontinent could have done much worse
As to "back to what it was before" - that is what the BJP is trying to do with its Ram Rajya and its movements against Mohammedans - namely turn the clock back to the power that was the nationS of India prior to the 8th century.
Though they, the BJP, are basically creating new history