I suggest
http://superversivesf.com/2015/09/12/is-khan-a-villain/ is a bunch of over-analized claptrap.
In the original series Khan was represented as a genetically created "superman," whose physical strength, endurance and IQ were superior to that of normal humans. IIRC* it was Spock who suggested that while certain "positive" qualities of humanity were increased by the genetic manipulation, so were certain negative characteristics --- like ego, for instance.
Despite the supposed superiority of these "superbeings," the apparant results of the "Eugenics Wars" on earth were as catastrophic to their empire(s) as Hitler's megalomania was to Germany and much of europe.
Why else would Kirk's first contact with them be after ignorantly reviving them after finding them in suspended animation in the U.S.S. Botany Bay, a ship used to escape from earth as a last resort? Hey, atleast Khan didn't bury himself in a concrete bunker with Marla the historian.....
Examining Khan's actions in taking over the enterprise show him little different, or more advanced, than a pirate, or any other aggresive, murderous villian suffering from sociopathy.
In the sequel movie
The Wrath of Khan Spock notes Khan's fighting patterns in pitting the Reliant against the Enterprise betrayed "two-dimensional thinking," a lacking one might think a genetically created superman with superior intellect would have overcome. Possibly though, Khan had little experience in submarine warfare, which would seem the nearest 20th century equivelent to (excuse the expression and crossiver reference) "star wars" stuff of the movie (sans X wing fighters ha ha).
Since JJ Abrahms movie basically had the same Khan as the TV series, I would assume he is the same there as in the TV series, the biggest difference being that since the timeline had been altered he was simply introduced through a different set of circumstances, and proved equally as nasty save with a British accent instead of a Northern Indian Sikh accent
.
I am not sure how Khan's character was
"poorly and inconsistently written." In both
"Space Seed" and the Abrahms movie Khan presented himself as, basically a polite, intelligent, inquisitive person at first blush, only to reveal his true intent later, though in
Space Seed he does offer a forshadow of what is to come when he remarks to William Shatner's Kirk how disappointed he was to see so little advancement in humanity since he took the long sleep.
Both Khans' behaviours seem relatively well written and consistant, just differing in a manner associated with differing circumstances.
So far as Kirk's "moral relativism" is concerned, in the movie it is apparently a "writer's construct" ....the TV series offers a great deal more to chew on if one doesn't limit oneself to the "Space Seed" episode, which does not itself portray any significant moral quandaries.
Just my two cents ....
*-- To be honest I don't recall right now if this happened in the TV episode or in James Blish's excellent novelization of said episode.