You talk about giving the developer tools, but those tools can be augmentations on top of the basic building block that is the language. That way, anyone can build tools for their needs, without complicating the lives of others. No need to build all the tools into the language, that's very constraining.
This is a thing that's commonly repeated, but it's not that, well, simple. Having a simple syntax doesn't matter that much for tools once you have a reusable parser library.
More important for tools is having a simple semantics. Do all builtins behave the same way? Is nil handled consistently (e.g. does indexing a nil map do the same thing as indexing a nil slice)? Are the coercion rules simple? Is importing a package free of side effects? (The answer to all of these for Go, unfortunately, is no.)
The most important thing, however, for tooling is whether the language provides static guarantees. For instance, if the language controls access to shared mutable state, you can do a lot to detect races statically. As another example, if panics were part of the type system, then you could statically know whether functions panic and, if so, what types of panics can happen. Here, Go provides very few static guarantees: it's very difficult to soundly prove anything interesting about Go programs.
Unfortunately, you can't really have it both ways: you can have a more dynamic type system that doesn't put many constraints on on programs, or you can have interesting static tooling. Go chose the former in nearly every instance.
That said, if you're trying to argue that autocompletion is more difficult to implement for Rust compared to Go because Go is simpler by some metric, then I disagree there too. Any static language (well, one that doesn't intertwine parsing and semantics like C++ does) can support autocompletion with comparable levels of implementation effort.
Anyway, regardless, there's certainly more work to do! And it's being actively developed quite heavily. For example, it will be on stable Rust very soon.