I really don’t think the inclusion of Kirk should be considered a “gimmick”. There was no stunt-casting, nor were the episodes in which he appeared particularly gimmicky (well, okay, “Subspace Rhapsody” was a gimmick episode, but in a way that wasn’t structured around Kirk specifically).
Like it or hate it, it’s clear to me that the producers are including Kirk because they think it’s worth exploring the character at this point in his career. I wouldn’t call that a gimmick.