If you can apply the term to every programming language in widespread use today[1], then yes, it is pretty useless. There is real value in having the term "functional programming" be meaningful and denote a certain class of languages; defining that as "any language with first-class function values" is too broad as to render the term meaningless.
[1] Even C has this with Apple's Blocks extension (http://clang.llvm.org/docs/Block-ABI-Apple.html).