If you go by fWAR, the Sox have the second best bullpen in the AL, behind NY.
If yo go by ERA they are fourth best, behind Houston, NY and Toronto.
Houston has fewer fWAR because the bullpen has pitched roughly 25% fewer innings. Toronto has a better ERA but less fWAR because their team ERA in the bullpen is a mirage. The Jays' relievers are walking more, striking out less and giving up more home runs that the Sox relievers. Their better bullpen ERA won't last if they keep pitching this poorly...