Because of --old-finders we need to support a lot of legacy code and dependencies. It also prevents us from following modern practices such as #2443

@staticdev what do you think about removing the flag? It has been five years since it was introduced as a fallback option after the breaking changes in isort 5.0. At this point I think it would be fine to do a breaking release where we remove it and clean up some of that old code :)