You can do it destructively when editing all notes at once, and even then, you are not bringing the velocity “ceiling” of the notes down. when multi-editing notes you add or remove values from all velocities equaly, effectively adjusting the “floor” instead.
I agree that a dynamic velocity “compressor” Midi FX would be at least ( if not more ) as useful as the current EQ Midi FX. In the old forum, I had a long list of interesting Midi FX that could be added to what the Pyramid can do.
You can also have a Sidechain Midi FX, which is really a Midi CC envelope. input is a stream of notes and velocities, and output is CC controlling the volume level of another synth. But you need an attack and decay parameter, because the input is a gate, not an audio signal.