Rosco, I do believe in defense, but I don't want to make incorrect assumptions about defense. For years in the NBA, you needed a dominate big man or the NBA MVP to win. However, in the mid 2000s, something weird happened in the NBA--big men stopped being good. They became less important because there were so few of them. In that wake (possibly caused by too many high school bigs going directly to the NBA), teams ran their offense through their point guards more and more. Suddenly, elite point guards became much more important to team wins.
That's all to say that, though there are many young big in the NBA today, teams learned how to win without them. Not that they aren't useful or valuable (they are still one of the most valuable assets in the NBA), but rather they aren't necessary.
That's my take on why we may not need an elite rim protector.
As far as Zeller or Olynyk goes, as a general rule, it takes more time for a big man to develop in the NBA. The older a player gets, the better his advanced defensive stats. You often don't see how good a big man will be until the middle or end of their second contrat (i.e. Favors, Jefferson, Milsap, Jordan, Ibaka, Hibbert, M. Gasol, Cousins, etc.)--that's at least 6 years of experience. Zeller and Sully are both on year 3. Olynyk is on year 2.
I would be interested in a rookie big man too--the right rookie big man. However, we need to understand that unless we luck into a player like Gobert, it will take us about 5-6 years before we see his potential reach his production.
At the same time, I like what I am seeing out of Zeller, Sully, and Olynyk as young big men. They each show the potential to continue to improve defensively (and not foul!). I don't think any of them are All-defensive 1st team candidates, but I do think they HAVE THE POTENTIAL to develop into big men who are solid enough to be bigs on true championship contenders. I don't think we will know for another few years.
Maybe I am loyal to a fault, but I would rather draft another big and stick with the bigs we have. Besides, I would really hate to see Zeller, Olynyk, or Sully picked up by a team like the Spurs and play big minutes for them.