That machine from a DA standpoint seems totally normal to me for a belt-drive, and I have A LOT of usage experience with them. My first use of a DA machine came in January 1983 when my mother got her first. I got my own in 1986, and have extensively used two others as well. As a matter of fact, it was AW.org that inspired me to take several non-DA machines out of mothballs to rebuild. Watching those agitators go back and fourth in one piece was almost 'odd' at first.
I will share a video I had put in my private collection from one of my own machines. It will show some of the drag that you're talking about regarding the auger moving backwards on BD DAs. This is not uncommon. The agitation stroke is such that it often 'yanks' the auger back a bit before it slips. This can be fixed to a degree by a little white lithium grease on the top of the agitator where it meets the auger, but is not necessary. There are only two agitator dogs or cams in the BD DAs, and they simply are not at precise as the DDs.
Here's a link to the video:
