I agree. They should have spent 3 hours on a flashback.
Various scenes they should have shown us, but were jerks:
1. Khan's mom is puffing. Khan pops out covered in slime. Using cgi eyelids and lips. he turns to the camera, winks and says, "I will have my vengeance!"
2. Khan is on the toilet reading the newspaper. Joachim knocks on the door. "My Khan, no one likes us. :sob:" Khan: "Damn! Ready the Botany Bay."
3. The Botany Bay lifts off. Khan: "Did anyone pack my porn?" :crickets: "Come on people!"
and so forth.