I'm a little late on this topic, but I just realized yesterday the step sequencer use a fixed veolicty of 100 for pads, which I believe is nowhere explained in documentation. For a moment I thought I had a hardware problem, quite weird as real-time recording had the pads giving me dynamic velocity.
Unfortunately the pad sound can change a lot with velocity. For example, in the Kit Core 808, the Bass Drum Kick sounds very sharp at velocity 100, and much gravier at velocity 60.
You can use the velocity MIDI effect or tediously adjust each step velocity but I found another way.
I found that on Push 2 you can hold SELECT down (with right hand), then hold the Kick Pad down (with left hand) : this displays the controls to adjust nudge velocity etc. Then, keeping the Kick pad pressed, you can use your right hand to change the velocity for all the Kick steps at once.