Can everyone be rich enough to not be in the bottom 20%? No, no matter how rich we become.
Can everyone be rich enough to have servants? No, unless you count machines as servants. But if you do, then I'm rich enough to have several.
You live way better than a king. Your expected lifespan is higher than kings because of access to better food, nutrition, and medical care. You have access to luxuries like chocolate, and coffee that kings might have tasted once in their life, or at best every few weeks.
Not understanding what wealth is, is precisely what leads to this mistaken thinking.
As for gentrification, it is often just confusing correlation and causation. People blame rich people moving in, when really a place just actually became better due to improvements in goods or services like public transit exapansion.
If I have a $200K net worth, and I'm living in a city where the range is $1M to $500M, then I'm pretty much living in poverty, even though I have "more wealth" than in scenario 1.
This is also why, although my absolute wealth today is hundreds or thousands of times more than a king in the middle ages, I'm not actually living like a king today.
It's also how gentrification works. You're living somewhere and all of a sudden a bunch of very wealthy people move in, raising the prices of everything. You're no more or less wealthy than before, but everything has become slightly worse.