To be honest it's less about their prospective play then it is about eliminating the Center position from the All Star Lineups -- even if they're posting gaudy stat lines they're competing for the same position in the ASG, assuming they're both still with Boston.
Completely agree with this - neither of them can hang defensively with big centers, and both will struggle at times with low-post defense, especially maybe KO, who is clearly to me a high-post stretch 4. At some point, the Celts may have to trade one or the other, as you so have wisely implied. However, I continue to stand by my original naked assertion. I see KO making a lot of threes and scoring a lot of points and JS sweeping the boards clean on a consistent basis. Is it possible that KO can average 17 ppg and JS take down an average of 10 boards a game? If so, then I think that would be a big step forward for each of them.