There are memos where Roddenberry, Fontana and Justman remark on the familiarity of plot devices being reused more than once or twice. They preferred to think of better and other ways of doing things rather than reusing previous devices. So familiar gimmicks being reused can often be traced back to Gene Coon.
Well yeah, Coon as show runner and script editor went through the multitude of script outlines and chose those which will pass through to the next step and become actual scripts. I don't blame Gene Coon if, because of the hours burning the midnight oil, he hadn't spotted that two or more scripts had former girlfriends of one of the main cast boarding the ship (one of the plot devices mentioned above), or the obligatory visitor from Kirk's academy days (so many of these), etc.
It's not easy at all to find new and interesting ways to introduce dramatic elements, Coon probably vetoed a hell of a lot more than we know of. Roddenberry and DC Fontana had a fresh eye and thus had an easier time noting the repeating elements.
And yes, using Koloth instead of Kor was a better option in the long run.