second thing I was just talking about Composite materials and remaining things about aircraft being static. You yourself stated that " it's just one part that can add advantages" then contradicts by saying that "capability of a fighter won't be changed much either"
Not really, I said composites alone don't change much at the capability of the fighter, as it is just one part of advantages. Add it with RAM coatings, ducted intakes and other signature reduction features and you have an advantage at RCS. Increase the engine thrust besides the weight reduction and you have a dramatically improved TWR...
If two aircraft's are same on every parameters except payload then not just for me but for others also one with higher payload will be considered superior because composite materials solve many problems starting from manufacturing to ease in maintenance.
First of all, a higher payload must not be the result of composites materials, but of any airfame strenghtening or thrust upgrades to the engine. Secondly, you are highly mistaken that the payload tells you how capable a fighter is, because it tells you nothing about the number of hardpoints, how many heavy and wet stations the fighter has and what weight limits these stations have. The Eurofighter for example has a payload of 7500Kg with 13 x hardpoints, which looks great on paper and for fanboys, but in reality the hardpoint layout was desiged for A2A operations mainly and therefor it has a lot of operational limitations in other roles (no dedicated pod stations, which occupies an important heavy / wet station in strike roles, the centerline station is highly size limited, the use of cruise, stand off or anti ship missiles is limited to just 2 stations, which leaves only a single possible config that offers very limited range...). The Gripen NG can carry more weapons, especially in deep strike config than the EF, although it has 1500Kg less payload and just 10 x hardpoints!
Lets come to what you compared about two different aircraft's built for different purposes: Multi-role capacity of Gripen C/D is far better than present JF17 Block 1...so your second claim is false.
Again wrong, because you must compare Gripen A/B and it's capabilities to JF 17 Block 1, or as I did, Gripen C/D to JF 17 Block 2, because these are the versions at a common tech and capability level and when you do that, you will see that the differences are by far not as bad as you think!
Third thing I am no astrologer so can't say whether one aircraft in development stage will be at par or will be superior to Gripen C/D.
You don't have to, there are a lot of infos already known about the Block 2 upgrade, check the JF 17 info pool.