It doesn't necessarily mean that the high performing schools are high performing because they have a high tax base, that's just a correlation.
Quality teachers may not be attracted to inner-city schools because of unstated biases, or because they prefer to live in other areas and have short commutes.
Or maybe you have a safety issue due to a school's location or an aging building and high rents that diverts resources towards countermeasures or repairs.
For whatever reason though, busing led to miraculously improved outcomes. Then we stopped doing it for some reason. Now, instead, we make some kids stay in schools where they have six hours of recess or lunch or study hall, then one session with a permanent math substitute with no lesson plans.
So yeah, funding isn't everything--but some schools can't even afford teachers for every hour of the day, or roofs that aren't collapsing. If there is a minimum threshold not being met, funding's probably part of it. The better solution is to just not bar kids who want to learn from functioning schools.