Its not a single unit, although they do do better higher than all the way down; its a dozen of these over the years that I've picked up and resold AND the one at the in-laws. Obviously, I have to test them out and usually they have to get a brand new belt and bag, so I know that's not the issue. I've felt all of them under perform even compared to my day-to-day Bissell Heavy Duty upright cyclonic ($130 from 2010 or so). Combined with the impracticality of the hose attachment and the weird sales model, it makes me kind of dislike Kirby on the whole, although they do seem to easily last a good 30-40 years, which is no small feat.
I'd put the pickup on par or slightly below my go-to canister, the Kenmore 116 series, which does ok but not great in most conditions.