KD majorly work best when used as a metric to save time weeding through thousands of keywords when doing your research.
The keyword difficultly metric is a complex algo that put a lot of checks in place. A real case example would be short tail / Seed Keywords.
Even a lay dude out there would understand the higher the search seed volume the more competitive the search would be , especially when semantic intent are in place .
Information intent keyword with 100,000 SV compared with a buyer intent keyword with same SV.
Using the case above, lot of websites would compete for buyer intent keywords to the information keyword within same cluster.
KD is a good metrics helping you filter a lot of time consuming repetitive tasks but shouldn’t be considered optimal metric for keyword selection.