It also means each time you create a new reactor, you never learn from past mistakes. Thinking that mass production causes more mistakes makes no sense when you actually think about it.

Cars/guns/airplanes/even furniture all benefit from mass production to keep costs and mistakes down. There's no reason why reactors would be magically exempt from it.

That's a massive benefit. That means there 10 opportunities to optimize the process.

The point is rather short sighted: after fixing the production line issue, you make another 100 and recoup the expense of those first 10.