actually if I remember correctly sasuke should've seen Kage Bunshin no Justsu waaay early when they fought Zabusa. He was wide awake. Aslo Naruto used it against Haku when they were trapped in the demon mirror. It was naruto's only move back then remember the good ol days

So my guess is those techs require a lot of chakra(which naruto definitely has more than sasuke).

So my guess is it requires a lot of chakra and control over that chakra. Sasuke just don't have the chakra yet even though he's uptill now been better at controlling his chakra.

I'm still not sure if sasuke will master rasengan, even though it seems like with enough training he should be able to. Maybe we'll learn more about it as time goes by or maybe they'll never explain it:/