As far as I’m concerned, Rocky V, much like Star Trek V: The Live Birth Abortion, is non-canon, never happened!
As for Khan becoming a White British guy, one line about how he was given plastic surgery so no one would recognize this FAMOUS DICTATOR could have at least explained that idiocy in reasonable way. But no, explaining anything simply wasn’t done in the Abrams movies.
Remember the line in TOS (Space Seed) where Kirk described Khan’s charisma as being “electric” ? Little Cousin Benny Cucumberpatch Walton from Walton’s Mountain had about as much electric charisma as a spatula.
“Rocky V, much like Star Trek V: The Live Birth Abortion”
Truer words have never been spoken.