Probably a lot fewer that works on the actual engine. And of them, none of them might be a DirectX 12 expert. Thats just what happens in real life sometimes.

Meanwhile there will probably be quite a few DirectX12 experts who play games as hobby, and have the know-how and a few hours to look at the problem.

Look I was taught and told that optimisation should be done at the end of development because if you refracter code to optimise it then there’s a chance that breaks something else and after continuing development the code you ‘optimised’ will end up being refractored again anyway (and probably end up less optimised).