I've not used McCalls before so don't know how their sizes come up.
Palmer Pletsch's 'Fit for Real People' compares the fitting shell/sloper bodices of the Big Four.
Vogue and Buttererick are identical.
McCalls are identical at the front, but a slightly shallower back dart which they reckon is not enough to make any significant difference.
Simplicity is similar although the side seams are slightly further back, but again not a huge difference. Could you guarantee that your cutting out is accurate to 1/8" on every single piece?
Lengthwise they are all the same.
Therefore any differences in the fit between the brands must come from the amounts of ease allowed in each design, and that probably comes down to the designers more than the publishing company.