Tarkin was completely unnecessary and a real blemish on the film. Leia could have been done with a hologram, but honestly I didn’t mind her at all.
It’s so curious that you didn’t like Tarkin but didn’t mind Leia. It was kind of the opposite for me. I minded Tarkin less and less as the film went on.
Difference of opinion I guess. You said it jarred you because the resemblance was uncanny? I thought she was fine precisely because it was only one shot, and there was no acting (which the CGI can’t emulate). She looked fine and not distracting. Tarkin on the other hand was in many scenes that required acting and besides, the computer was not as good at rendering Peter Cushing’s angular and gaunt facial features as it was Leia’s rounder and softer features. But maybe I just didn’t have time to pay close enough attention because it was just one scene.
Just my opinion.