Expecting Sweeney to be able to aff 3 top 6 players with speed , jam, and more skill, plus 4th liners, plus 2 defensemen is unrealistic to say the least. You are basically asking Sweeney to draw to an inside straight, and really longer shot than that.
As it would mean convincing people to take less money to come to Boston, and doing it 5 times over, in a market with very few good free agents, and an ridiculous number of teams with an insane amount of money to spend. And yeah trading Ullmark might get you one of those pieces, but that's about it