Agreed, D is a much bigger and complex language than Go.
Comparing the standard libraries, Phobos doesn't look far behind Go in scope. There are big holes though, like crypto, which is entirely missing, and a complete SQL driver (was in development, but we haven't heard from it for a while now), although there is a binding for SQLite3 and several drivers for major RDBMSs (not in the standard lib, tough). Logging will be included soon.
Most of the rest is included (networking uses libCurl), and Phobos quality is continuously improving, some parts of it being excellent both in terms of functionality and performance, like the new regex library. On some other parts, like containers, Phobos seems much more advanced than Go. OTOH, there seems to be more 3-party libraries for Go than for D, but we can't comment on their quality. And of course, both languages allow to bind C libraries.