This is a fair point except that neighborhoods are not fungible and are in short supply.
You’re assuming that there is another 3/10 neighborhood available for the people who are displaced to move to, and therefore they gain a short term benefit and eventually end up back where they were.
In practice it’s typical that older areas which have become run down have ample city services, such as transit, parks, and libraries, which may not be the best quality, but at least exist.
Since neighborhoods are no longer built with these amenities, the best available substitute for someone who is displaced from an old neighborhood may be far less desirable than what they had before - a 1/10 trailer park, or worse, homelessness.
However, if we would continue to build traditional neighborhoods that were walkable, had city services, had transit etc. and built enough of those to keep up with the demand, then it would be much more likely that your scenario would play out. In that case the harm of economic change in neighborhoods would be greatly reduced, perhaps even to the point that it wouldn’t be a problem anymore
But that’s quite far from the reality on the ground today.
Transit comes with density and growth and usually increases in property values. When an area goes downhill but still has this services it creates a temporary situation that people can take advantage of certain aspects - live with increase crime but get increased services.
The wealth of yesterday created that situation. At some point someone will invest in that older area because of the location value.
The only way to artifically control that is through low rent units. Which create other barriers because one can never leave or they give up something even though it might make sense to move somewhere else for family or job reasons. When they always take 1/3 of gross getting a raise and taking on more responsibility seems counter-productive. Hard to break dependence.
You’re assuming that there is another 3/10 neighborhood available for the people who are displaced to move to, and therefore they gain a short term benefit and eventually end up back where they were.
In practice it’s typical that older areas which have become run down have ample city services, such as transit, parks, and libraries, which may not be the best quality, but at least exist.
Since neighborhoods are no longer built with these amenities, the best available substitute for someone who is displaced from an old neighborhood may be far less desirable than what they had before - a 1/10 trailer park, or worse, homelessness.
However, if we would continue to build traditional neighborhoods that were walkable, had city services, had transit etc. and built enough of those to keep up with the demand, then it would be much more likely that your scenario would play out. In that case the harm of economic change in neighborhoods would be greatly reduced, perhaps even to the point that it wouldn’t be a problem anymore
But that’s quite far from the reality on the ground today.