The key word here is "role" replacement. Su-30, Mig-29 and Rafale cannot replace the Mig-21 by role. Only LCA, F-16, Gripen, Mirage 2000, F/A-50, J-10 and JF-17 can.
The issue with LCA Mk1 is both versions sit between the JF-17 Block 2 and Block 3. Upgrading the IOC to FOC standards will take time as well, plus the squadron is needed in Sulur. So only the FOC is available, and there will be 16, not 20, enough for just 1 base. Similarly, it's unlikely for the IAF to afford to give away more than 1 squadron for this role, even that's too much.
So 2 squadrons with detachments will be enough only to deal with something like the post Balakot skirmish, not a war. For war with Pakistan, we will need at least of 4-5 LCA squadrons. It will take us 3 years to get to the minimum necessary.
Let's not forget that without the LCAs, it will be very difficult to use the Jaguars in the strike role. Su-30, Mig-29, Rafale and M2000 are needed for their own missions, and with the exception of the Su-30, all other aircraft numbers are in a deficit.