kakashi reminds me of one of those kids in elementary school who is far ahead of everyone else so everyone thinks they're a genius, but by the time high school rolls around, and everyone else has had time to bloom you realize he was nothing too special, above average yes but nothing phenomenal he just had a fast start instead of a late bloomer he was an early bloomer.
What I'm trying to say is Kakashi started out strong but in the end his max potential/ceiling was never that high people only thought it was because he had a strong start.
Take Naruto for example, his ceiling is way higher than Kakashi's even without Kurama, but he didn't truly become strong until he was 16 he was a late bloomer. Talent and potential are tricky things