iaf did not employ the mig 21 alone but was part of a high low package, where it formed the low part and the mki was high part and was to provide top cover to this package, But due to effective PAF jamming the mkis turned back while abhinadan didn't, guess being a senior officer.they will claim it was abhinandan's jet , went way off course.
Mig-21/F-7 are best used as point defence interceptors. No point in trying to upgrade them if they are nearing the end of their service life.
IAF thought it could keep 21s relevant by adding BVR capability , R-73,77 etc. Too many limitations in terms of fuel it can carry , small nose cone (small radar) the list goes on . why do they deploy Mig-21s in front line if they have 270+ Su-30s ?
This in theory is a very effective strategy if employed in unison.