Q sector of vendor management

How do you think about the quality of your suppliers? You need some kind of measuring stick to compare the quality of supplier A and supplier B. One idea is the following 5-level scale. 5 is excellent, 3 is the normal pass mark, and 1 is no good. What do you think?

5 CPK is 1.66 or higher, and quality control targets are linked to business targets

4 CPK is maintained at 1.33 or higher.

3 There is a quality control department and CPK is managed, but it is below 1.33

2 There is a quality control department, but management is not done using statistical methods

1 There is no quality control department