I doubt Wiemer repeats AA and if he does it is not as big of a deal as you are making it out to be. AAA isn't really all that much more advanced than AA is. AA has far better talent in it than AAA does unless you believe players like Kelley, Singleton and others are better talent. AAA baseball is basically filled with players like Kelley and Singleton which are basically roster fodder for the MLB teams. If Wiemer has to repeat AA which I doubt he will it wouldn't be this huge negative and wouldn't decrease his value all that much.
As for a trade for Devers if this is what it would take I would do it right now but I think Boston would want something more if they are trading Devers.