In the past year I've worked with a couple of codebases upgrading multiple versions, and it wasn't that much work. The upgrade generator lets you step through each changing file, view diffs, allowing you to edit files manually if you edited the core config files extensively. In general, the more you edit those core config files instead of extending via initializers, the more painful it is, so perhaps you've worked with codebases where there wasn't a lot of discipline.