um sasuke can control the cursed seal now and he can use it whenever he wants. its a boost in chakra and makes you stronger...who wouldnt want that..and oro might be half dead but hes a sannin.
sasuke could own kakashi..sasuke doesnt "require" the cursed seal 1 its not like a must...he is using it to boost his chakra kinda like a buff...you dont even know anything about the shinobi he killed...plus, why would he be trainning on weak shinobis...that makes no sense..even if he were...