All valid points, of course. Things aren't looking great for Zeuch but he has some unique characteristics that, I think, make it worth holding out hope that even without a big developmental leap he might be capable of MLB SP production similar to, say, Kendall Graveman for a few years while he's still cheap.
I'd rather have a durable back-end SP than a stupid groundball reliever guy. And of course if he flops in 2019/2020 you can always throw him into the pen at that point and see what happens.