Having previously owned the SM3 and now UM3X, I will not say SM3 does everything better than UM3X. For example, cymbal sounds "further away" on SM3 than UM3X and sounds "blunt". On certain tracks, I can barely hear the cymbal's presence on SM3 whereas on UM3X, though the volume may be soft but the cymbal makes its presence due to that "cutting edge". Sharp edge but not piercing at all.
When it comes to vocal, on the UM3X, the singer is felt to be standing before the instruments
whereas the opposite is felt on SM3. This is not necessary better or worse but I like a more forward vocal.
With regards to bass, I feel UM3X has tighter but leaner bass and does not extend as much as SM3. Impact-wise, both are about the same.