OMG! It seems you're out of touch about Aerospace industries!LOL.
F21 is just another F16 avatar. It is black listed in India. Game over.
SH18 is a old horse, even in a block IV or V.... the latest swisss eval, this year, show that SH18 is low agile than legacy F18. It is heavier but with less load than Rafale. It's just a stop gap fighter, so are the capacity.
Beyond superficial reassembles of F-16, F-21 comes with APG-83 SABR AESA and same EW Suite as F-35. The armaments package is unmatched. The most importantly, F-21 comes with MALD-J for swarm attacks against s-400.
https://www.globaldefensecorp.com/2019/08/01/lockheed-martin-f-21-meet-make-in-india-fighter-jet/
Super Hornet is semi-stealth and proven platform, can carry Nukes.
https://www.globaldefensecorp.com/2018/05/31/boeing-f-a-18-advanced-super-hornet/
Both F-21 and Super Hornet come with ToT. Rafale is great fighter aircraft, no doubt about it. Rafale is omnirole as well but costly to acquire. Question: Can India afford whopping £8B again for 36 Rafale or for 100+ Rafale costs whopping £50B plus. Indian would rather buy F-35 if they have to spend £50B.