I have the New MiniI as well. I have found that the vacuum will suck right up until the bag is stuffed full and dust begins to fill up the hose.
The suction does drop as the bag fills, but I've never used a vac of any size/quality where this isn't the case. Depending on the nature of the dust it can happen quicker or slower as the bag clogs up.
I have found the filter clean function (aka filter bag cleaning function) does a good job at increasing suction levels again.
I also think that one's evaluation of performance can vary depending on the situation. I use my vac all day in the workshop without issue, but when I'm cutting inside someones home I'm suddenly acutely aware of all the tiny particles that manage to escape the vacuum's draw.
Don't expect miracles from vacuums, it's a tough ask to suck up all that fine dirt all day long without letting any of it back into the air and maintaining full power at all times. . . but send in ideas on a post card if anyone has a better design
