I understand your concern. Perhaps the answer is just that it is hard to make a perfect assessment of a situation like this.
The Congressional Budget Office in the United States has done some work on this. They make exactly the same points. They say that the situation is very difficult. They analyzed all the job creation reports. They analyzed the work done by the United States Government Accountability Office. The conclusions are very simple and take up only three pages. It is very difficult to use examples and reports per project in order to do an overall calculation of the impact on employment or of the results of these kinds of initiatives.