As I've been saying for years, Boston should be doing everything possible to maximize the Jayson Tatum championship window. If that means they sell, they should. If that means they buy, they should. If that means they do nothing, well maybe they shouldn't do that, but if that truly does, then they should. This team needs to maximize Tatum. They've needed to do it since basically the summer after his rookie year, and they just haven't done it. Tatum is Boston's shot at a title. Maximize his chances of leading the team to that goal.
I agree with your general idea that we need to maximize the Tatum (I'd say Tatum & Brown) championship window.
But when is the optimal part of that window? When they are in the primes of their careers, right? It's pretty widely agreed upon that an NBA player's prime is between ages of 26-29.
So my thought is we need to ensure that we set ourselves up to maximize those seasons -- which begin around the 2022/23 season. I think in order to maximize that window, we need to have a good supporting cast around Tatum & Brown. Not necessarily superstars, but good role players. I look at the continued development of our current young guys like Time Lord, Pritchard, Grant, Nesmith, and Romeo into solid NBA role players as the key support to maximize that window, along with retaining Smart, and landing other draft picks and MLE signings and trades at the time to fill the gaps.
This mentality is why I don't get too upset over losing streaks right now. I think we're still in a development stage for this team, rather than a "title-or-bust" stage. I think our best years are ahead of us and we can't make impulsive moves now that will set us up to be worse when our franchise players are in their primes.
Lebron and Durant will have aged quite a bit by that time too. There will be new stars (Embiid, Jokic, Doncic) to contend with of course, but I don't foresee them becoming the all-time great players like Lebron and Durant will go down as. This makes our championship probability even higher at that point, IMO.