Melt? at the speed with which someone opens a folder I do not think you need to worry about melt or soft vs hard. Bearing systems move easier, with less friction, hence their use. Bushing systems take heavier loads with more friction, hence their use in suspension systems. Look under your car or truck and the majority of partial rotating/pivoting components have bushings not bearings. The can take much higher loads due to the flat surface area having much larger force distribution. A ball bearing system would likely be destroyed by suspension loads due to high point stresses on the ball bearings.
Hardness is irrelevant when you have a flat piece against a slab of handle against a blade flat. It is like a sandwich with layers all pressed against each other. A bearing system has bearings with a single point on each ball bearing touching the surface area. Force is much more evenly spread on a bushing than it is a ball bearing system or even cylindrical bearings. Just simple statics. Each ball takes one point load and the overall force is distributed over however many ball bearings you have.
In a knife's case, I don't think there is much of a difference, but there is no doubt that the load on a bushing is distributed more evenly over it's larger surface area than a ball bearing system.