The Yankees just took on $295 mil for Giancarlo Stanton. I'm skeptical that they can turn around and sign Machado as well, especially with their overriding need being starting pitching.
Whichever team Machado signs with, it will go against the grain of their history. So the Sox are no different than other teams in that regard. The difference is, the Sox will have little to nothing committed to their payroll, and could afford Machado and still have an average or below average payroll for a few years at least.
As for him upgrading the Sox roster. That is 100% irrelevant. We aren't trying to win yet and his future is not here. I'm also skeptical that he could ever be a tradable asset to other teams.
If JR wants to do this, great. But I'm not expecting this nor will I call him cheap over this.