Chamber pressures and velocity are directly interrelated - you cannot separate the two. All other things being equal, higher pressures with the same bullet, in the same gun, will produce higher velocities. Lower pressures will equal lower velocities.
But, technically speaking, it is neither pressure nor velocity that wear out a barrel or cylinder, etc. It is GAS CUTTING, referred to as "barrel erosion". Nevertheless, barrel erosion has a linear relationship to pressure/ velocity. Higher pressures = higher velocities (with a given bullet weight, etc.) = more gas cutting/ faster erosion. So, lower pressures = lower velocities = slower erosion.
There are other factors that have an effect, such as jacketed or cast bullets, bullet fit, how smooth the interior barrel surfaces may be, etc......in other words, friction-related items. Lower friction = slower rate of wear (obviously). These will have some effect, ultimately, on barrel life. But, a relatively small effect. The overwhelming issue is erosion due to gas cutting.