Let's assume everyone else agrees with every point you have raised, but especially the desirability of getting both Arroyo and Duran onto the big club.
Given that, wouldn't it be worthwhile to explore why Bloom and Cora, who have been monumentally successful retooling this team this season, have chosen not to do so?
I am very possibly the least expert contributor to talksox, but even I can identify a couple.
One is that these Sox are on a five game winning streak and have the highest winning percentage in the AL and 2d highest in MLB. Don't mess with success.
And they are doing this despite some issues with the rotation, which neither Duran nor Arroyo can fix.
I also don't see other one improving the sometimes spotty defense significantly.
That leaves hitting, and right now the Sox the Sox are 2d in MLB in scoring and 3d in OPS. That said, I too would probably rather see Duran or Arroyo in the batting order than, say, Santana or Gonzalez or even Chavis. And my guess is that Arroyo is a good bet to return when he is healthy and ready.
As for Duran, however, I kind of like the outfield of Verdugo, Hernandez, and Renfroe, whose WAR's, in order, are 1.6, 1.4, and 1.5. In a very small sample of 3 games, Hernandez just might have solved the leadoff problem--he's 6 for 12 with a walk.
None of the above is intended to say Arroyo and Duran should not get to Boston this season, but only that waiting a while longer doesn't look very risky.
I leave to others the larger considerations of salaries and other GM-related issues.