T-Max 100 and Acros 100, and Ilford Delta for that matter, have rather similar grain structures to one another. If you compare them to a traditional emulsion like FP4+ or PlusX, they will look quite different.
It also depends on how you're scanning. If you're using anything short of a very high end scanner, then odds are you're seeing digital noise superimposed on a partially resolved grain structure, in part because the grain size will be smaller than the true optical resolution of the device.
Finally, I have drum scanned a lot of my own B&W film lately (generally at an aperture of 11 microns, which is larger than most B&W film grains), and I find that the grain structure of Tmax is very hard to resolve (at least grain for grain) as compared with FP4+ and HP5+. And and if on a drum scanner I'm having difficulty actually resolving Tmax grains at 11 microns, then I have my doubts that you're really seeing the grains unless you happen to be using a drum at 6 or 3 microns to do your scanning.
That said, I don't really care about the grain structure. I actually find the look of Tmax and Acros quite unappealing, and I find that the darker shadows and brighter highlights on these films have a lot less detail than I'm used to getting from other films.