According to the Indian AF, MMRCA is a Mig-21 replacement.
I tried to find a citation of the above but found the one below instead.
"the MRCA tender was floated with the idea of filling the gap between its future Light Combat Aircraft and its in-service. The IAF planned to replace the MiG-21 fleet with the indigenously-built
HAL Tejas (LCA) aircraft. "
So I think they are not doing an apples for apples but re configuring for the current scenario where Mig 21 - 27 and the Jags will be retiring to be replaced by a single aircraft to carry that load.