If your outbound flight to India was so delayed, why did you not look for alternative options to reach India. You were in paid business and could have essentially FORCED United to book you in a similar class on any other airline. Leaving from EWR, you had so many options, LH/AI/LX. Looks like you insisted to stick to your original itinerary. Secondly, if UA put you on UA48, they would have told you about it and explicitly shared that you had Economy seats. And Y class is NOT BASIC ECONOMY!. When offered the UA 48, why didn't you ask for the DEL flight instead? Also, since you were choosing to go via HKG, why didn't you ask them to reroute you through JFK or IAD where you could have potentially gotten on CX's superior business class service.

At this point, you can file for downgrade compensation, though you have to be careful as they might claim the Y ticket you were booked in was probably more expensive than your original J ticket. If you have booked your ticket with a suitable card that offers delay compensation and baggage delay compensation, you can claim damages from there as well.