I also wouldn't worry about redundancy, hurting development, or anything like that at this point. The reality is that someone is going to get hurt. Most likely, multiple people are going to go down at the same time. Whether it's for the whole year, a few weeks, a month and a half, you get the point. If Johnson doesn't get playing time next year, it's his own fault because whoever we sign as a center is going to be injury-prone (looking at targets), KG will probably have a minor bump and bruise somewhere, Sully has a bad back, etc.
Bottom line, we need all the talented players we can get. If they fit together perfectly, that's just gravy.