That's the same mistake we did with LCA and Kaveri, thinking it needs to be 100% Indian and kept „hoping“ on it, but the engine, the radar and so many other things are only subsystems! The only thing that matters is, that the fighter is designed and developed by us, according to the requirements of the forces and suitable to our needs in geographical or climate related sense.
Nobody cares if the Gripen uses an US engine, nobody cares if J10, 11 and 17 uses Russian engines, nobody cares if the Korean T50 uses a US engine, Israeli radar and so on..., all that matters is, that we get the fighter project done!
We will need a lot of work to get Kaveri to a level to power the Migs, if we can improve it to power AMCA is a long shot and needs to be seen. That's why even recent DRDO officials seems to seperate the AMCA project from Kaveri (but it's DRDO, lets see when they will come up with the next dream) and basically confirm foreign engines for AMCA.
The F35 is a stealth fighter but that's it, while Rafale offers far more NG capabilities. So NG is not limited by the airframe shaping and the Silent Hornet without the need of external fuel tanks, with internal weapon carriage and upgraded avionics will have several NG features too, that's why it would be the best compromise for us. The best NG fighter remains the FGFA, which is not "only" a stealth fighter, but a true NG fighter.
It's not about the size, but if the aircraft is designed to be used with catapults or not. The Mig 29K or Pak Fa are not, if the Russians develop EMALS, they will develop new AEW aircrafts for the use on them too and most likely suitable UCAVs.