I've got a Jam2 and have no complaint about the rear suspension.
In general - journalists/reviewers are stupid enough to point at stuff, that are easily fixed, and give a negative score.
Who cares about default tyres, default grips, default suspension setup, etc....that are easily fixed..??..
So it's much better to come here and ask the real users
I've set my sag and rebound etc as per this vid on my Jam2 and all was good. I did notice the rear wheel "cones" nut was loose so giving some movement. They are not cones on the rear wheel but there is a nut on each side of the hub that needed to be nipped up.