Do we know that it was Meyer specifically who added that idea, rather than the earlier writers like Harve Bennett, Jack Sowards, and Samuel Peeples?
No, not that I'm aware. I'm just making an assumption. Meyer says he took concepts, plot points, characters, etc. from the other drafts, but that the dialogue was all his. I just assumed, therefore, that Khan's explanation was written by him. But you're right. It could have been anyone who contributed to any of the drafts including, as mentioned by
@Maurice, possibly some influence by Roddenberry.
I'll never understand why people think TWOK is "a great film" -- I find it achingly stupid on many levels. The inanity of the planet-confusing business is just a symptom of its larger brainlessness.
Because it is entertaining. It is well acted. It is suspenseful. It has a marvelous score. It does the characters justice, especially the "big three." And many other reasons.
Of course there are aspects of it that are mind-numbingly dumb. I agree with you. For example, you are told that Khan put creatures in the bodies of Chekov and Terrell to control their minds, and no one bothers to do a scan on them? Heck, I can even nitpick small things like being able to take over a starship by remote control with nothing more than a five digit numeric code, and there being a dedicated panel of numbers at the weapons console specifically to allow punching in such a code.
But none of that stupidity bothers me enough to affect my enjoyment of the movie because, well, it's a movie. And this is where you and I have been disagreeing. I think Star Trek should follow real world science where it can, but I don't think real world science should trump making a good movie. If they need a silly explanation for mistaking one planet for another, I'm fine with that.
So yes, certainly ST was never a bastion of hard science fiction. But its contemporaries in 1960s-80s SFTV were so much more mindless and nonsensical that ST deserves credit for even trying at all to get some things relatively right.
I agree with this. There is a happy middle ground, though, somewhere between
2001 and
Lost in Space and I think that is where Trek landed. And I'm fine with that. I don't think it took anything away from Trek that Roddenberry didn't go to Kubrick levels of concern for scientific detail when making the show, but I agree it's good that they strove for more scientific realism than their counterparts over onboard the Jupiter 2.