The thing is Indian UP work with settled GPs, and AI *loves* to settle GPs. It's not uncommon for my England/Turkey to conquer an Indian city and find 6~10 GPs settled in them. With their UP it means they can work 5 tiles for each of their cities and still pump out wonders faster than anybody else.
The Indian UP needs to be modified to *NOT* work with settled GPs, and/or to give less food per Specialist, and/or have an upper limit. Seljuks never does anything to India in any of my games - on the contrary it gives India a chance to take Persia easily. Mughals just replace India, inherit those GP infested cities, and build more Islam wonders - as I have shown.
All European conquerors except the Spanish are pathetic. They barely have tech parity with the Mughals (who start with Gunpowder, and have an awesome Cannon UU) or even the Indonesians (who usually wipes out the Dutch conquerors in my games).
I don't think it's about earlier civs being more powerful on Epic/Emperor either. My Japan, for example, thrashes China easily each and every time and I've won Domination as Turkey before 1800. It's just the Indian UP - it becomes really, really OP late game. It makes Statue of Liberty look pitiful.