No, Ziggler is NOT expendable when you only have the Smackdown roster to pick from; You said it yourself - Baron Corbin is supposedly one of the top 6 guys on Smackdown - Can you really spare Dolph when your top end talent pool is that shallow? He will be utilized; I do however understand entirely how you feel, Dolph has been push-teased, and then relegated back to the midcard so many times, and for a very long time, its the people around him that made me go "Wtf are you doing? He's very important now, although I don't think he'll be given the title(yet) I do think its a step in the right direction for his career. Considering Roman Reigns was pinned twice, clean in a 48 hours period, I really feel like anything can happen in WWE for the first time in a very long time.
The leash seems to have been lengthened regarding everything - promos and storyline are seeming more intelligent, in-ring promos are back instead of being exclusive on the WWE network .... I could go on, but the change is obvious
Raw is the established roster; Smackdown is a hybrid of youth - and veterans to try and create new talent and try new things - the group they have on Smackdown reminds me of the first time they did a brand split - Raw looked totally stacked compared to Smackdown, but thanks to some great veterans like Undertaker and Kurt Angle - they were able to build up new Talent like that John Cena guy.
The split should(IN THEORY) give the writing team more time to focus on a single show, It should give the wrestlers themselves a bit of a break and in turn increase roster durability(Which honestly, it wouldn't surprise me to find out that THAT was the whole reason behind this draft and split)