I also think you have to consider the purpose of the establishing shot. If it is just meant to be a buffer for pacing, then you really could use any establishing shot. But if you wanted to make it clear that they’re supposed to be on Mustafar, then reusing a shot might be the simplest way to make that clear to the audience.
It would be preferable to have a brand new shot, but it would require some vfx work if you wanted a new shot, but also add Vader’s castle.
Not trying to argue, really. Just trying to say the pros and cons of the different options.