So a couple of reactions to points made.
Yes, there was something mentally off with the team last season. Too many sleep walk games where they lost to far inferior opponents. But I am chalking this up to the abrupt coaching change a couple of weeks before the season started. I think this had an impact but it wasn't apparent until the end of the season. I think the focus and compete every night attitude will be better this season. I think they learned their lesson on that front.
As to leadership of Tatum and Brown, this is going to fall mostly on Tatum. Leaders aren't necessarily born or developed, it is some of both, but that type of leadership takes time to be learned. Not every player has it in them to be a leader, but even the best leader takes several seasons to figure it all out. The time for Tatum is now and this is related to the point above. Tatum needs to set a "all business" tone, every game, every quarter even in his quiet low key leadership style. Coaching is part of this too.
As to the comparison of the 2021-22 Horford-Williams vs. 2022-23 version, I don't think it changed all that much from an offensive standpoint. Horford was the scoring big, Williams was the defense and rebounding big. Both declined some, Horford due to age, Williams due to injury but Horford shot 44.6% from 3 for the season in 2022-23, and was a steady 10 pt/gm scorer. Williams was not 100% in the playoffs in 2022 either. But Williams injuries led to us playing the small line up. It was the defense and rebounding that was lost when you had White on the floor over Williams. White is a good defender but a different kind of defender than Williams. You just can't play the same team defense when you take out Williams and put in White.
For this coming season, Porzingis can be the scoring big, there will be way less pressure or need for Horford to score. Last season we were kind of forced to play small, the most used line up was White-Smart-Brown-Tatum-Horford, which of course is indirectly related to lack of depth in the big rotation, which was the result of Williams being injured or not 100%. Horford can be the D/Reb big this season for the most part but also pitch in with decent scoring along the way.