So pretty much, I've heard things like the the older RD (300,800 ect) series and older MP (MP8, MP5) series and then compare them to things like the RD2000 and the MP7/11, Ive noticed that those older stage pianos sound way more realistic and sound more convenient. Even the strings/pads, they sound super professional and the newer ones sound very synthy (I'll demonstrate in a video on another subject for a question on my MP7SE). For a while I was turned off by Yamaha because at one point, they didn't carry a lot of (or any at all) harmonic/string resonance and made a lot of playing seem super computerized even though the samples itself sounded realistic. But now they're starting to incorporate that in their sample-based products and sound amazing. Is the newer lines of keyboards sounding synthy temporary? I'm really starting to consider going old school and getting a older keyboard for certain uses and keep my newer keyboards to practice technique on. Is this just me though, or do other people notice this as well?
You and all of us have grown up believing in an illusion: that things arise out of their components---that cause gives rise to affect: double the cause is doubling the effect. This world in maths is called the linear world, and in science we have a major principle called occams razor. Occams tazor neatly fits this illusion of linearity: if there are lots of ideas about how something might work, the simplest one is most likely.
In this world, if sampling rate doubles, we should feel the sampling has gotten better and as the sampling rate goes up, our perception of the improvement should be linear.
This isn't how the real world works---you do not judge the new by its improvement on the old; rather, the old imprinted on you, and the result is the thing that judges the new sound.
Non-linearity results from interactions between components that aren't necessarily foreseeable in advance, but lead to emergent outcomes.
In otherwords, the past changed you, and that alteration changes the way you perceive the new information. In the non-linear world, the input (cause) drives the system to create an output, but the output changes the system or becomes an input ie feeding back into the system.
Imagine a block of Jelly. You heat up some water in a kettle. You dribble some of the hot water onto a teaspoon and then gently move the teaspoon over the jelly. Then you turn the teaspoon and poor the hot water over the jelly. It hits the jelly and melts the jelly at the contact point. This creates a valley in the jelly in one spot. When you repeat this process, if you tip the teaspoon of hot water over the jelly near enough to the previous spoon's spot, the new hot water hits the jelly but quickly flows down the depression left by the previous spoon's water dump. This melts the jelly creating a deeper valley in the same spot rather than creating a new depression at the new contact point.
This situation is non-linear because the past has affected the present such that new information (input) gets processed differently.
This non-linear characteristic of human consciousness means that after being exposed to one brand's piano sampling, one can find a rather different brand's sound source synthetic, thin, etc. Not only does this non-linear nature cause us to prefer one brand over another, but it can cause is to favour older sampling over newer sampling; favour older sampling over newer sound modelling etc.
This is why we also tend to prefer music from our era over current music, and/or get influenced by our parents records which permanently changes one's taste in music.
We don't hear what is, we are what is hearing (encoded in memory), and the past has made our memory which we use to hear with.
It's not a phenomena limited to hearing. People find others who look like their parents younger self more attractive than people who do not, and why we find those who are unusual to us to be unfamiliar, causing one to be wary.
That said, it is possible to acclimatise to the new. When I got my MP7SE, I hadn't sold my MP7 yet. At first, the MP7SE action felt alien to me, and the sound was so different, I didn't immediately feel it was better. I kept playing the MP7SE and comparing it. After a while, listening to the new sound, I began to hear subtle aspects of the sampling that the older sample doesn't have. Over time I felt better about the action. I had about 6 weeks with both instruments and by the end, I preferred the MP7SE. I also had the ability to play the same sample using different actions, so I started to acclimatise to the new action.
Perhaps if I hadn't had both instruments to compare for quite a while, I might have kept a rose tinted view of the MP7.
I'm quite sure if I was given a Casio PX-S7000 and had long enough with it, I'd eventually see its subtle natures and enjoy the sample despite it not being an SK grand.