Think the classic BPA argument is being misused a lot in this thread, there is absolutely the case where drafting a player by fit is beneficial to both your short term chemistry and long term talent flow.
We already have Isaiah, Bradley, Smart, Rozier, Hunter, Jackson, Young. The rotation is young, competitive and above all else flexible. We have depth in case anyone breaks down, talent developing in the D League, and the luxury of having one able to step up as a replacement if any of them are going to be used a trade.
Adding Dunn would have forced us to accelerate some decisions that we're not ready to make yet. The next big trade could easily be months away and we need each one of our backcourt players for potentiall ammo/salary matching. By not giving up playing time to Dunn we can showcase the trade candidates and not worry about any behind the scenes griping about PT in the locker room.
In this way of looking at it Brown could be 70% the player Dunn is and it would still have been the right call, BPA should always be used when your team is not close to contention, you ignore things like positional redundancy because it's likely few if any players on your current roster will be on your final team. The Sixers are better off loading up on all of those Centers because talented 7 footers are easy to move and will always be coveted. When your on the short list for top teams in your conference like we are, you have to keep the good of the team in mind.