Tsarkar-> in this case I disagree, the Derby was never really required by the IsAF, it was for export markets, it was developed from the Python IV, removing fins and with a Radar seeker. The Israelis always had access to latest Sparrows and Amraams, they developed Python III/IV/V etc. initailly since till early 70's they did not have AIm-9 series missiles and till the AIm-9X came along the Aim-9L and AIm9M lacked a bit compared to the R-73's.https://www.flightglobal.com/rafael-unveils-open-secret-derby-missile-a-decade-late/37255.article
The missile is the standard radar-guided weapon on Israel's Lockheed Martin F-16s and is carried on the same pylon as Rafael's Python 4 imaging infrared guided dogfight missile. Derby was developed in the 1980s, says Rafael, and has been in service for 10 years.
Derby is 3.6m (11.8ft) long, has a diameter of 160mm, the same as Python 4, and weighs 118kg (260lb). The missile is slightly narrower and lighter than AMRAAM, but about the same length.
Plus being 80's vintage, I am sure propellant tech has also moved on, it is as best a stop gap measure, what Tejas needs is Astra integration and orders for Astra in numbers which in turn are produced fast. Till then the Tejas in A2A will be more or less relegated to Mig-21 Bison role although they will perform it much better.