All i know is that J10b is far better than JF17.
If the OP pertain Fc20 to J10b, then JF17 will be no rival.
Which is a clear overestimation, especially when you consider a JF 17 Block 3, with a similar technical level.
If you look at both from PAFs point of view today, the advantage of J10B is not be that big. The fact is:
- JFT B3 should have IRST, IFR, similar radar and a reduced RCS as well
- the weapon package will be exactly the same (in PAF, including indigenous missiles or foreign additions)
- the weapon carrying capability will be 90% the same (only in LGB strikes or with very light bombs J10 has an advantage)
- radar and avionics will be broadly the same too, if at all with a bit less performance for the JF 17
The range and flight performance needs to be seen, when more reliable specs about it's weight and thrust will be available, but that will be different for a JF17 B3 as well, that might get WS13 by then. So all in all, it comes down to the delta canard design, the lower wingloading and maybe some TWR improvements, that will add to J10s A2A capabilities, but other than that, there is not much difference for PAF by chosing J10B.
Regardless of the media speculation, the J10B upgrade is not really a comprehensive one and that's why the difference to JF 17 is not bigger. The most crucial problem is, that neither the fuel capacity wasn't increased (be it with CFTs or bigger internal fuel tanks), nor additional hardpoints were added. That limits J10 to 3 x wet stations and the same fuel tank or weapon configs as JF 17! J10 is meant to be a propper medium class fighter and should offer a clear weaponload or range advantage over a light class JF 17, which isn't the case, while RCS reductions, upgraded radar, avionics and engine capabilities are normal for any upgrade and are expected for JF 17B3 too.