Whether or not you want to admit that the characters' shared history -- in particular Kirk's shared history with both the villain and with Spock -- were important to the dynamics that made Wrath work... they were. You're mistaken. How do we know this? We know because switching Khan out for a random slightly-rewritten player and running the same basic set of beats was tried. It was called Nemesis, and well... you can see how that worked out.
Nice try but no. But you get an A for effort.
"Space Seed" had no barring on their "shard history." As I already stated, the pivotal plot point(s--and cause of Khan's hatred--occurred completely off-camera. They existed solely in a few lines of exposition.
This would have been no different if they made up a bad guy of their own, and audiences would have perceived him any different from just about every other one-off movie bad guy who, told his story, muwa ha haed, and set out for revenge.
Even the McGivers connection is dubious at best. There is zero evidence she was even the wife in question. They weren't married at the end of the episode, and she's never mentioned by named in TWOK. It's just common assumption.
Greg and others have since "canonized" her as such, but that was all after the fact.
TWOK was written to exist solely on its own. How do we know this? Because a studio would never put out a film where the plot and conflict were dependent on a 15 year old story from a different medium.
Any perceived "significance" to the use of Khan is solely due to existing emotional attachment to the character. It's why Bennett chose to use him. As did Lindelof.
Oh, and...
The Nemesis example is so tangled in fallacy, I'm not going to dignify it with a response.
Khan's personal traits: intelligence, strength, ethnic/religious background, etc. had no impact on the film whatsoever. All parts of this statement are demonstrably false. (They're to some extent true of CumberKhan, obviously, but not the least bit of his predecessor.)
How exactly?
His ethnicity and religion were never brought up. We were told he was really smart but never actually presented any signs of intelligence. And his only "feat" of strength was lifting the charred piece of space junk off of Joachim. Except, in a world with force fields, see-though, super strong aluminum and thingamuboper alloys, there's no way to know just how heavy that thing really was. An even if it was as heavy as one would assume, lifting it really wasn't anything a fit normal human couldn't do under the influence of adrenaline.