You just proved my point
The Su30 served as a blueprint as a base for the J16. You didn't start from scratch like lets say America did for F16.
S400 is a relatively newer variant, China has S300 and SAMs based on it (i think its called huang qr sam or something).
India does the same thing. I did agree that currently industrial output wise China has a lead over India but India has the lead over the ability to source weapons from multiple sources, also actual weapons difference is not that high (Indian airforce is lacking full operational capability though).
Missiles, Navy and Army are mostly fully operational with new stuff being inducted.
Biggest playcard here is the US and how far they'd be willing to sell India stuff to keep China in check.
So far we have Chinooks, Boeing personnel carriers, Airbus personnel carriers, Apaches, P8Is, possible induction of Stryker APCs with TOT, MQ8 reaper drones and more deals in pipeline. We have major ongoing deals with other European powers too.
Russia is currently in talks with newer Brahmos missiles and for more Kilo class submarines with India.
Afaik we're in talks with France for their submarines too (we already have some inducted).