Great, that parallels my experience too. When I got my new Aristo SD45 and my new Dash 9, they ran like crap out of the box and I wondered what the heck, since they have 12 wheel pickup.
Since I had experienced the sintered wheels from AML, I quickly removed that coating, which all I can surmise is to protect until sold.
I reckon they got pretty shiny, although on magnification you should be able to see that it is not "solid" steel.
Here is a picture of a late model Aristo SD45 with sintered wheels.
Without aggressive cleaning, this is after 2 hours of run in time:
Clearly mechanical abrasion is necessary.
Greg