The path I wish we had taken was never trading for Kyrie at all. Kyrie had serious red flags in Cleveland (freezing out teammates, wanting to be "the #1 guy" while playing with the league's best player, wanting to leave a title contender etc.).
Keep that last Brooklyn pick, draft Shai Gilgeous-Alexander and this team would have been set. That also would have allowed for retaining Rozier as a bench scoring presence. Or the pick could have been an asset for trade.
The entire premise for trading for Kyrie was to attract Anthony Davis to play here, AD, as a Klutch client was never going to be routed to Boston. Ainge misread the room and the Kyrie mistake then led into worse roster moves - the Kemba signing/losing Horford, trading Baynes attached with a #1 (that turned into Desmond Bane) and then having to attach yet another #1 to get rid of Kemba (that turned into Alperen Şengün).
I know that's easy to argue in hindsight and no guarantee that Gilgeous-Alexander, Bane or Şengün would have been selected. But certainly there would have been more assets and likely a deeper roster.
I suppose the takeaway here was the build up assets/stay flexible (for star trades) approach while grooming the young high-potential guys came with trade-offs. And the downside/opportunity cost of that approach has been realized.