I'd give more weight to how Scotty is set up as the villain - as what's told is as crass as it is contrived: McCoy states a female coworker bonked him on the head by accident and now he hates all women, so naturally the first place they go to is a pleasure planet chock full of women (was Redjek controlling everyone to a lesser degree on the ship simultaneously?)
MCCOY: My work, Jim. This is prescription stuff. Don't forget, the explosion that threw Scotty against a bulkhead was caused by a woman.
KIRK: Physically he's all right. Am I right in assuming that?
MCCOY: Oh, yes, yes. As a matter of fact, considerable psychological damage could have been caused. For example, his total resentment toward women.
Wow.
That simple, is it? McCoy is real hot to trot this story plot point... Of course, is it really plausible?
Possibly but under a set of criteria that 10 seconds of throwaway dialogue isn't going to convincingly convey. So is it stretching plot credulity?
Completely. The story doesn't even bother, hoping what follows will remain compelling - and to its credit often does, but not completely. Never mind that we all know that every time a female character is put on screen, she's going to be murdered. The psycho-tricorder also makes its first... and only use and I'll get to that in a tic...
Having Redjek's ability to hang out in computer circuits explained might help as well - yes, there are some great moments but how this incorporeal form can scientifically piggyback microchips as easily it does for brain chemistry and still retain its ability to do whatever the script needs... it could have been a lot more throwaway, but the initial shock - and Spock defeating it with Pi - is still a delight that outweighs the questionable moment.
So I'd fix those. Build up the plot a bit more nuanced and rely on either Redjek controlling multiple beings with less dominance and thus be easier to overtake (and that's not as much fun anyway) or spend time explaining how it can count up CPU cycles in the computer hardware's spare memory bank. The former, by far, is preferable, despite the loss of the Pi scene (which is still so well-acted. John Fielder is so underrated as an actor, but as character actors go one couldn't do much better.)
Pretty much everything in this scene rules. Acting from all, voice echo effect, overall tone and content... creepy stuff.
Also, about Pi...
So about psycho-tricorders... "Turnabout Intruder" would have resolved the story's big question about Janice/Kirk a lot easier than Spock's mind meld, though for dramatic reasons the mind meld works in this story's favor as Scotty points out it's not evidence. (Though CMO McCoy could still relieve Kirk under proper suspicion?)
As well as for the other plot issue in avoiding the reveal of Janice's claimed insanity, which is for the best no matter which way would have been used and if it's true the suits didn't want female captains, though given what else season 3 talks about it's clear nobody cared about the show by this point and the story itself proves it. This story can't make up its mind whether or not it's tackling the show's sexism, 23rd century sexism despite showing how humanity fixed all its other problems before then, paralleling late-60s sexism in real life on top of the show behind the scenes, if Janice is legitimately insane, or what not... and the latter issue is still the focal point to the story despite the others. The story showing her being insane, or at least bordering it, narrows down the narrative but those social commentary plot points remain floating as worse as unaddressed than an elephant farting in a peanut bar. If they didn't care about the show, Gene should have just put out what he wanted for a stronger story narrative to end the series on instead of his hodgepodge.
