Just by chance I ran across a documentary tonight on Epix called "With Great Power" about Stan Lee, and Lee is pretty explicitly giving Kirby total collaborative credit, saying that he designed those characters, and that the interview that led Kirby to leave Marvel (because of the way Kirby was portrayed by the article) wasn't even going to have Kirby in it, but Lee didn't want to be interviewed as the sole creative element at Marvel because he worked so closely with Kirby.
I haven't paid all that much attention to this apparent dispute, but it's hard for me to imagine Lee giving Kirby much more credit than he does in this documentary.
17 minutes in here:
https://www.youtube.com/watch?v=jvgjca9gKnM
Maybe Marvel itself has a different POV, but I don't know that your representation of Lee jives with this.