No way I'd walk away from what he has. Unless he has an unlimited budget.
You have a much better start than I thought you were going to have (and a better set of toons than I do, but I digress). Build up your Phoenix (probably won't be able to 5* thrawn unless you buy some packs during the event, but he might be useful to you at 5* to go with Palpatine, Vader). You could use tarkin who you have at 7* and I see you got a 2* Sion now. I like Nihilus over Sion personally, but can't go wrong with either on that team.