[Bionichute]

I would argue that the prevalence of the sixth ranger archetype exists almost entirely because of Power Rangers. The Green Ranger was immensely popular, and Dragon Ranger was the FIRST sixth ranger, at least the first to actually stick around for more than one episode.

Zyuranger is obviously still the basis for the concept, but you can see there was still some hesitancy to the concept through Kakuranger and Carranger, which didn't really have proper sixth rangers. This also happened during the time where Power Rangers and Sentai were airing alongside each other, so it's highly likely that this was a massive factor in sixth rangers continuing to be a thing, and reaching the level of marketing that they have today.

Power Rangers has also definitely affected anniversary seasons due to how the two franchises have lined up, even up to Zenkaiger. Gaoranger's anniversary tribute was a movie, Boukenger limited its references to the monster designs, Gokaiger was only originally going to have anniversary episodes for the series that had mechs based on them, which were all ones that got adapted into Power Rangers, and the only Zenkaiger member not based on a Power Rangers adapted series was Zenkaiser.

I know it's silly to say that Gokaiger made steps to ensure that it could be adapted into Power Rangers considering how it went, but I really doubt that they would have expected it to go like it actually did.

I think Power Rangers has had a marked impact on Sentai from a production level, if not a story one. Power Rangers being made is the exact point where Sentai stopped being able to make things like Jetman, where it shifted to more generally family friendly material. Some people probably don't consider that a good thing, but its definitely something that has worked out business-wise.