All that old information is terribly confusing, but it's not entirely useless. GOPATH is still critical, as it's how you can run fully-offline builds of Go programs and override dependencies without changing the root project itself.
This isn't accurate: `go mod vendor` will dump the dependencies into the vendor repository these days, so you can build totally offline. There's also a mechanism for renaming dependencies (so you can replace them basically).
Not quite: both vendoring and the 'replace' directive in go.mod files (which I presume is the mechanism for renaming dependencies you are referring to) both require modifying the root package.
With GOPATH, I can package a single library and use that package to fulfil the dependency on the library of any other Go application offline. Conversely, with the vendoring mechanism, the Go tooling will need to download (or copy from cache) the library when you originally create the vendor directory or when you add a new dependency to the root project.
