I'm not sure if a car seat is allowed in place of a stroller 'above' your baggage weight restrictions based on your cabin class - we were under our weight restrictions even after checking in our car seat with our luggage.

We did BOM_DXB_LHR in June this year and carried both a stroller and a car seat with us. We checked in the car seat with our luggage at BOM and kept the stroller with us until we reached the boarding gate. Just before entering the aircraft, they took away the stroller for loading into the luggage hold.

Just FYI, at DXB there are complementary strollers for use so DXB wasn't a problem at all. At LHR, we were told that we need to collect our stroller after we cross immigration and with our normal luggage so that was a bit of a walk.