Your two reasons nailed it quite right.
But there is another thing. Fighter jets are not produced like hamburgers.
Before you can produce one, there are thousands of components that have to be fulfilled. No use having 10 production lines, when you cannot produce enough engines for example to use it all up.
The quality controls are there. For one thing, and you have to give credit to the people in charge, everything now has to pass through a strict rigorous process of certification, quality testing and control. For example, the engines recieved from Russia will have to be individually tested again and certified by the Chinese, those that did not perform to meet standards will be rejected and sent back. You cannot mass produce to an extent and hope you can keep your quality up. The Soviet Union at one time, produced as much as a hundred Flankers a year, but I bet a lot of it were junk.
Now there is another thing. The PLAAF itself cannot absorb or digest 100 new J-10s a year. That's because an organization can only change so much. At best I can only see them changing two or three regiments per year. Actually PLAAF modernization is organizationally quite stressful, since overall, one regiment each have to also convert to J-11, JH-7A, even J-7G and J-8F respectively. For that reason, you can aslo see why the PLAN cannot absorb so many new ships and subs.
Its just like a human being. No matter how many hamburgers you can make, you can only eat so much.