TG-
Verily, I have read some of the stuff you are referring to, and Bagley's book, etc.
I recently read Solie's interview with the HSCA, in which Solie comes off very poorly, and cannot explain why he believes Nosenko on the JFKA/KGB. You might get a kick out of the interview.
https://aarclibrary.org/publib/jfk/hsca/secclass/pdf/Solie_6-1-78.pdfSince we do not have accurate organizational charts of the KGB circa 1963, I cannot prove Kostikov was Dept. 13. The biographer quoted above, who claims to have been friends with Kostikov, says he was Dept.13.
I take it you never met Kostikov, nor have seen accurate organizational charts of the KGB circa 1963.
Bruce Solie as a KGB asset sounds plausible, as does the KGB running LHO, possibly through G-2 assets in the US, which by most accounts had thoroughly infiltrated the Cuban community.
That hardly proves the KGB/G-2 had a role in the JFKA. But, I wouldn't rule it out, either.