His appearance in itself wouldn’t be fan service if he did something of value to the plot. Mon Mothma and Jimmy Smits weren’t fan service. They had a tangible purpose in the film. I’d have much preferred Vader to the cartoon Tarkin though. His lightsaber battle actually might have been better had he been built up in the film itself and not just thrown in there under the assumption that he’s the most badassest villain in the galaxy.
Agreed. The final moment is the most obvious reshoot too.