A real piano is also profoundly lacking in expressive control over timbre (excluding extended techniques like half-pedaling or directly touching the strings that hardly ever show up in the repertoire). The only control the piano gives you over note timbre is how hard you press the key. Once you've done that, the hammer disconnects from the key and flies through the air out of your control.
A keyboard with polyphonic aftertouch, such as the Yamaha CS-80 (famously played by Vangelis), is objectively more expressive than a piano.
> The only control the piano gives you over note timbre is how hard you press the key.
This is just not true at all. The action of a piano is a very sophisticated mechanism that conveys both acceleration and velocity, along with the initial position of the key (e.g. fully released or half-pressed). This allows for a huge amount of tonal variation, though it's more subtle than a ribbon controller, and obviously a synth can do many things than a piano cannot.
All the complexity you mention only affects how the repetition lever (part 9) briefly bumps against the hammer shank (part 8). The only information this imparts to the hammer is velocity, and once it happens there's no more contact until the hammer falls back down. The hammer can't somehow remember what caused it to travel at a specific velocity and strike the string differently. There's only a single degree of freedom in its movement. What you perceive as "a huge amount of tonal variation" is mostly note timing.
It's entirely true for the attack, because of the escapement mechanism. At the point at which the hammer makes contact with the string, the hammer is mechanically disconnected from the key and moving purely through inertia. Once you've tripped the escapement, the hammer is beyond your control and pure physics takes over; the only variable is the velocity of the hammer when the escapement is tripped.
The release phase is controlled by a single parameter, albeit one that can vary over time. The key is holding up the damper, which returns to the string under gravity. A continuous value representing the range of motion of the key would be sufficient to model this with absolute accuracy. Digital pianos invariably sense release velocity rather than key position, because it's much cheaper to implement and is perfectly sufficient in virtually all cases; the range of motion between partial and full damping is so limited as to provide only a very limited degree of expressive control.
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A keyboard with polyphonic aftertouch, such as the Yamaha CS-80 (famously played by Vangelis), is objectively more expressive than a piano.