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.