Agreed, Third Nacelle. My point was that Trek has a huge canvas now, more so than it’s ever had before. If you’re going to reintroduce Khan, why not give the new audience something the old audience was never able to see – namely, more of Khan’s epic origin? And as has been pointed out, it didn’t need to take up a huge amount of screen time – it could have been shown to us as Khan “narrated” his story to Kirk once he revealed who he was. A few scenes showing him in power on Earth, then being forced to flee, then the Botany Bay being discovered would have fleshed him out and made him feel more like Khan.
That and, as I pointed out, better dialogue. Montalban was charismatic & grandiose, spouting one classic line after another. Cumberbatch was cold, ultra-serious and wasn’t given any great, memorable lines. And not seeing his people revived just feels wrong too.