This seems to be an illustration of the following: gentrification only leads to displacement if housing supply is scarce. This can be caused by extremely high demand (Manhattan would be expensive even if there were no zoning controls, simply because building skyscrapers is expensive) but more often than not, at least in the US, it's caused by restrictions on density — this is true in Lincoln Park and Wicker Park for sure, where neighbors keep blocking even moderate density near transit. In places like Cleveland and St. Louis, since they've been shrinking for so long, there's no shortage of housing supply, and so revitalization can happen without displacement, even in the absence of enlightened policies on density.