The max TDP they can cope with before going over a set temp will vary with so many things, ambient temp, case airflow, CPU die area/TIM, thermal paste that I don’t think it would be a useful number.
Still it generally gives you a rough idea as to what you are working with. I'd rather have some kind of representative figure of some kind than not.
And just like in cars, if one manufacturer is honest and other not, it will distort comparison.Indeed, it is a bit like manufacturers stated fuel consumption on a car.
It may not be an accurate real world figure, but it does give you some guide and allows you to compare one car with another...