I wouldn't say that Power Rangers was a gateway to tokusatsu, but it made it more acceptable in the US (but people still only recognize it as a superhero genre, and not a special effects medium). Before that, it was Godzilla, Ultraman, and other Japanese sci-fi movies & shows that made it here (in context of TV shows, it's only a handful, in comparison to the near-hundred shows most Americans have never seen).
I never once needed Power Rangers to be introduced to tokusatsu. When Power Rangers first came out, I was insulted, because I had already seen Zyuranger a year before (and was already familiar with Super Sentai, thanks to Dynaman), and considered it to be an infinitely superior program. Power Rangers, in comparison, was an embarrassment and insult to the original. While it's "cool" to most people here, I still see it as a bastardization of Super Sentai (which, itself, is not getting any better now).