[IIsi50MHz]

This isn't quite correct, or at least not for the reasons you've articulated. "Weighted" versus "semi-weighted" has no such inherent limitation of ranges or values, even leaving aside that the numbers you've chosen are probably simply for the sake of your example. The actual limitation between most weighted and semi-weighted keyboards is that semi-weighted tend to have inferior sensors (and possibly other components), because these instruments tend to be marketed towards people who desire to spend less money on an instrument. There is no technical or physical limitation that requires semi-weighted keyboards to have less expressive range.

Unweighted keyboards tend to have simple springs to return the keys to resting position, and more importantly, the cheapest instruments tend to only have note-ON;note-OFF characteristics due to being unable to sense any variation in how a note is played. These instruments playing all notes at the same volume is a natural consequence of inadequate sensors.

Returning to your sample values, MIDI 1 only directly supports 256 levels of volume, I think? This 8-bit level of variation is far lower than what any normal human sensory input can be expected to discern. MIDI 2, which was still very rare when last I paid heed, is a substantial improvement for potential expressivity. But even many years later, most consumer-grade instruments and playback devices only supported MIDI 1, sometimes with extensions such as GS or XG. The most expressive of the pro or semi-pro instruments that I've experienced have only seemed fully capable when using their internal proprietary enhancements; when outputting to a MIDI 1, the results were much less impressive.

As an aside, I've played only one piano whose keys felt as lightly weighted as my first semi-weighted keyboard and I found it a delight to use. Fully expressive, and less effort for the same effect as other pianos. I felt like I could play it for hours without tiring. By comparison, keys on all other pianos I've tried now feel quite heavy. I wish I could have afforded that one at the time. Sadly, memory of its make and model are long garbage collected.

[crazygringo]

> There is no technical or physical limitation that requires semi-weighted keyboards to have less expressive range.

Of course there is -- it's not a technical limitation of the instrument, but of our physiology.

If there's more weight resisting, this gives us a wider range of control, for the reasons I explained. Of course only to a point -- once it gets too heavy that a light touch can't move it, or the heaviest touch becomes too fatiguing, you've gone too far. But pianos are weighted in a way that approximately maximizes our level of expressive control without being fatiguing.

So yes, semi-weighted keyboards inherently have less expressive range. I mean sure, not if you're a robot playing with infinitely fine motor control. But for actual human beings, semi-weighted are absolutely less expressive. There's no getting around it.

And with regards to the one extremely light-touch piano you found a joy to play on -- I'm quite sure that it couldn't have been played extremely softly in an even way. That's just the inherent tradeoff. If you're playing music than never goes to ppp then maybe you didn't notice. But I don't need to see the piano myself -- this is all just physics and physiology. It's inherent to how it works.