Tour grading

Can I suggest that the grading be based on someone’s FTP or there last previous race. Someone who can maintain 3.9 w/kg should not be able to self select in D grade to blow everyone off the road. Maybe something like if they achieve 0.5 w/kg over the grade range then that grade is closed to them in future until they have a race where they finish an event with an average power within the grade range.