Mishap, it isn't about a simple measurement against national targets. It is much more about progress data. Schools are now able to measure progress against similar schools, so for example, if you have a high-achieving cohort on entry at KS2 you have the data to measure levels of progress against schools in a similar socio-economic group for pupils of similar ability (though it is much more complex than this simple description), We used to do this for the schools in our LA with a local "basket of seven" schools, but now there is national data available. Ofsted uses this extensively and masses of data analysis goes on before the inspection. The analysis of progress used by the school leadership and the measures put in place as a result of the analysis very important.
Ofsted inspectors simply do not work as you describe, in my experience. It is a rigorous and careful process. Yes, inspectors sometimes get things wrong; it is a very pressurised process. I have done many inspections (LA and Ofsted) and I simply don't recognise what you are describing. It is a very intense and stressful experience for schools, but at the end of the day, you are there for the children. I have seen people very upset by Ofsted, but many, many good schools who are thrilled to have their achievement recognised.