Nah. It's not that Llorente is overall an inferior striker to Vucinic. It's just that Tevez and Mirko are technically gifted and intelligent enough to form a very good partnership, that will work better than any other partnership we can have in attack. That's the reason why Mirko will keep his spot in the starting XI.
Tevez is the clear star of our attack, so Conte will pick Tevez's partner depending on Tevez's needs and characteristics. That will grant Mirko the starting spot, even if Mirko isn't vastly superior to the other attackers. It has nothing to do with Conte having a soft spot for Vucinic. Mirko will be out the moment someone else contributes even 1% more to our overall play and attack. Just that I don't see such a striker in Juve atm.