Yes, the rich get richer and the poor get richer too but the poor feel poorer.
We are not just talking about the poor but the working class and the lower middle class. They see those above them advancing faster. Their perception is that they are relatively farther behind those ahead of them than in the past. They feel like they are losing the race.
Not saying you are wrong but you don’t address the relative perceptions. The media feeds these perceptions.
You even noted that the rising tide lifts the rich boats much faster than it lifts the poorer boats. This means that those below the median fall farther below the median just like those above the median rise farther above the median. With an ever increasing range from low to high, the hurdle to achieve the next level becomes taller.