The more important issue maybe the powerplant rather than anything else. CFT's are not like drop tanks and cannot be jettisoned in flight. This means that whether empty or filled they are a dead weight on the fighter. I am not sure if the CFTs for the J-10C create drag.. but they will require a slightly more powerful engine.
Fair enough and I share the view that the emptyweight and partially the lack of thrust are the main problems for J10, but the added weight of CFTs are mainly used as an argument during close combats, while the overall pros and cons will be ignored.
With CFTs, J10B...
...wouldn't need the twin pylons for BVR missiles in CAP, because the inner wingstations could be freed from fuel tanks => reduction of weight and drag!
...would have a lower RCS in interception and CAP roles, since it requires less or even no (depending on the final capacity of the CFTs) external fuel tanks anymore => BVR advantage!
...would be able to carry more heavy weapons in strike or anti ship roles including a full AAM load => propper medium class load capability!
...could extend range and endurance of operations => advantage if such a wide area must be covered and to reduce the number of tankers that are needed!
Wrt the weight addition, the B upgrade is said to include weight reductions as well, so the addition of weight of CFTs should be at least countered by that too and even if the same engine will be used and no drag benefit would be achived (which would be surprising compared to external fuel tanks and pylons), the weight should not had been a real issue.
So even if we say, weight is added and one can't jettison the CFTs during close combats, they do add a lot of other advantages, which makes them overall far more useful than carrying external fuel tanks and limiting weapon loads.
J-10C completed Maiden Test Flight and with that also got IOC, FOC and all the OCs and is now fully combat ready unlike other fighters around the world which takes a ling time to get OCs!!
That works both ways, the one side that is jumping the gun because some fanarts of CFTs came up and the other side that still underestimates the Chinese and their impressive industrial capabilities. The fighter is ready today and the B version is reportedly in serial production, the CFTs however are not and that's what I pointed out. However, I have no doubt about that China will develop them much faster again than many people believes!