Quite frankly, this doesn't make sense to me. He's a great fit with that team. Their half court died in the playoffs and Dame would unlock that. Dame is what they need.
You must have forgotten Kemba Walker. Or Kyrie. Neither of them fit the "timeline" of the Js. Neither has Horford yet how many years he's played with the Js? Timelines are over-rated. No team has the same age starters running together for a decade. That's a thing of the past with mega contracts of today. Dame is 30. He'll be productive for the next 3 years before drastic decline like Lowry at 35/36. Lowry won the chip when he was 34. Nobody said he was on his decline in 2019.
If dame had been available before the porzingis trade it might have happened. Now I doubt Boston could make it happen without giving up Jaylen Brown since most of their other assets are gone.