That's like saying G.I. Joe isn't really "West" because it was co-produced by Toei.
Yes and no. Transformers figures began as Japanese toys (mostly created by Takara), as opposed to G.I. Joe toys, which purely originated within the U.S. TF certainly holds a stronger presence in Japan and has a much more "native" feel (thanks also in no small part to numerous Japan-only/Japan-initiated iterations of the brand). Taken strictly on the merits of the original TV show, though, the Toei co-production wouldn't be enough, true.