No, templates are only needed to introduce new symbols. And D templates are vastly superior to C++. D's superpowers are CTFE, static if, and static foreach.

auto is used as a return type because it's easy, and in some cases because the type is defined internally in the function and can't be named.

You would not like the code that uses auto everywhere if you had to type everything out, think range wrappers that are 5 levels deep.