The part within your title stating if one could easily use Mangekyou Sharingan even without being an Uchiha is not fully accurate.
While Kakashi does have the [Mangekyou] Sharingan and can use it's abilities, it is not without a cost. Because Kakashi is not an Uchiha, using the Sharingan takes a huge toll on him.
Because he isn't an Uchiha, he can't deactivate the Sharingan and it rapidly drains his chakra whenever he uses it, leaving him bedridden after extended use
(emphasis my own)
Orochimaru did not want only the Sharingan - he wanted the full power of the Sharingan. It is for this reason why Orochimaru was interested in an Uchiha's body as a vessel rather than the eyes by themselves. If Orochimaru had only taken Sasuke's eyes, he likely would have experienced similar side affects as Kakashi.
Orochimaru could have done some experiments to give himself the ability to deactivate the Sharingan at will in the same way as an Uchiha. However, due to the lack of Uchiha to harvest DNA, Orochimaru saw taking the entire body as the solution.