Bad gouge above..major has ZERO bearing on service assignment from an NROTC standpoint.
The only thing major does have a bearing on is selection for an NROTC scholarship.
Is this relatively new? Admittedly it was another decade, but when I did the paperwork for service selections, major was a factor. Not a substantial one, but as was mentioned before, there were three Tiers and you got some points added based off your Tier. Again, grades and CO recommendation were the things to worry about, but major was factored in.
They may have done away with this now, but I'd kind of doubt it, as it's another way to force-shape.