> vim [...] extensible IDEs that support code completion, folding, and navigation by default.

If "by default", you mean "with the default vim configuration", then this assertion is wrong.

Vim does have a definition-search" feature, but it needs hand-made configuration for each language, and since it relies on regexp instead of parsing the language, it's useless outside of micro projects.

To enable real code completion and navigation, vim needs plugins and external tools. The modern way is to use one of the LSP implementations for vim (I've tried ALE and CoC), but that's clearly not "out of the box" for vim.