pianoloverus She was not talking about hybrid actions. In her video she is using a Yamaha Clavinova at home, and grand pianos at school. The Clavinova has a folded action, like the majority of (non-hybrid) digital pianos, which is made of plastic and (some) wood.
Since I have two digital pianos now, one with plastic folded action, and one with full-length wood action (not hybrid), I find a lot of things DariaPiano said valid, and makes sense.
Action: Acoustic piano keys are harder to push, but easier to hold. Digital pianos are the opposite.
Folded plastic actions has lower moment of inertia (due to plastic's light weight) compared to full-length wood action. This means when strike for high velocity (e.g. f or ff), finger don't feel as much resistance as acoustic action would have. To remedy this, heavier weight is used on the "hammer". As a result, static down weight (the force to barely move the key) is also increased. My FP-30X's folded plastic action's down weight is 10-15g more than my MP11SE (full-length wood non-hybrid action). FP-30X is easier to push (at greater than mf), but harder to hold, whereas MP11SE is harder to push (at greater than mf), but easier to hold (and play softly).
Dynamics: Acoustic is unlimited in the upper (louder) dynamics - the harder you strike the bigger the sound. Digital piano dynamics has a hard limit that's easily reachable.
Digital piano definitely lacks in dynamic range. I can see the MIDI value (i.e. velocity) produced. There is definitely a hard ceiling. Both of my DPs MIDI tops out at about 120 (out of 127). I can drop a brick on to the keys and the sound it makes wouldn't be any louder.
Timber: Acoustics timber is not only rich but completely controllable by the player (you). Digital piano uses recorded sample so at any certain dynamics, the timber of the sound is baked in.
This has improved over the years, but still a valid concern of all sampled libraries. Due to file/memory size limit, it's not possible to record samples at all possible velocities. Instead, only several (between 4 to 25) select velocities are sampled. Lesser sampled sound engines may only play a sample at different volume to fill in the gaps, resulting lack of timbre richness. More sophisticated sound engine blend sample of adjacent velocities to make timbre gradation more natural.
My Roland FP-30X's built-in sound clearly lacks timber richness. It is the main reason I quickly switched to Pianoteq, a modeled sound engine that does not have this problem. The sampled sound in the MP11SE is more sophisticated - its SK-EX sample is pretty good. I also bought the widely-praised VI Labs Modern D library - it is considered one of the best, if not THE best, sampled piano sound. That said, if one buys a digital piano and only use its built-in sound, chances are the lack of timbre richness is a real issue that would negatively affect intermediate students and above.
