Unfortunately, I for one, can't answer your question. I've never seen a 2500cc chainsaw in the flesh let alone used one.
My chainsaw is about 35cc and it runs as smooth as you like. In fact i'd say it does in fact it does run smoother than my Rocket 3, but maybe that's because it's small and light by comparison.
It sounds as though the bike is not living up to your expectations.
Some Rocket 3's transmission/final drives do appear to report to run coarser than others, but how true in reality that is, is not scientifically proven.
The first 2.5 Rocket I rode I also thought perhaps a bit 'rumbly'. It had 6k on the clock. So I tried a new one out the following weekend and it felt good. I then (1 hour later) jumped on the first bike I tried just to compare again and it felt just the same.
I ended up buying the 6k one and it's very nice. I'm happy with it.
I think the only one who will ultimately know is you unless there is a more detailed and specific characteristic you can somehow describe.
That said, there may be someone who will chime in with wisdom beyond my experience.