There are various reason I ask for JF17 B3 over J10C ,
1- Price, we are short on money that why our government want to make deal with the west to ease sanction and get some money ... (JF17 B3 would be 40-45 million $ per full unit package, while J10c would be 70-80 million $ per unit, remember Im talking about full package), we need 4.5-5 billion $ to get 100 JF17 B3 and addition 1-2 billion $ to get 4-5 KJ500 AWACS and command controller platforms ...
2- Quantity and maintenance, we need at least 100-140 fighter jets with low maintenance and fly cost to cover our sky for 24/7 in span of 2-3 month, 40 J10C are not enough
3- political reason, selling J10C in meaningful number will change the balance of power in Iran favor in region and for sure, so many countries will oppose it and put pressure on China to not sell or just stall delivery which make acquiring J10c in short span of time ( less than 2 years ) very unlikely unless China is willing to take the pressure ...
4- Pilot training, from years ago, we are sending our pilots for some additional training to Pakistan, so if Pakistanis agree, we can use their existing training capabilities to train our pilots and shorten the time for integrating JF17 B3 to our AF ( we need train the ground crew as well )
5- We have active order for 40-60 Su35 , so buying another expensive 4.5th Gen fighter would put so much pressure on our AF which is always short on funds...
6- The era of 4.5th gen fighter would be over in next 5-10 years, so spending so much money on 4.5th gen fighters is insane!! We should go for J10AE , Su-57 or Su-75 if the producers are willing to sell 5th Gen fighter with acceptable condition to us.
Lets be honest , China is not willing to commit to any seriouse military deal with Iran till the JCPOA end and we don't have money for it ...