If it were grain aliasing, or scanning artifacts, to me that implies that it's not an apples to apples comparison.
Even if the scanner is incapable of resolving the grain of all films used here, a comparison could still be made. But that ASSUMES all other things being equal. I have scanned TMax 400 many times, and some frames come out very smooth, and others do not, and it always has to do with negative density and contrast. Very dense negatives frankly scan very poorly, and those are the ones that come out looking grainy.
Rule number one when comparing two films, regardless of what the output is: the negatives should be photographed in identical or highly similar lighting conditions, AND developed to the same contrast.
If care is NOT taken to accomplish highly similar negs, then it is NOT a meaningful comparison. Period.