The problem with these kinds of lists is that they often are written by people in order to appeal to the "nostalgia" within their readership, those who probably have no idea that Power Rangers continued past Wild Force,... or In Space,...or "that series with Robot Dinosaurs and that 'awesome' evil Green Ranger," while similarly getting trapped in blind nostalgia themselves often by relying on similar "pure childhood recollections" and little, if any, research outside of photos for the article.
Linkara has himself noticed, that a majority of the people commenting on his History of Power Rangers Series notably stopped watching shortly after the early Saban seasons, or even the very first season, as they "grew up," or "forgot about it," and are quite frankly surprised there was more to Power Rangers then their childhood memories, or pop culture, suggests.
Then there is the difficulty in arranging multiple series of a long running franchise in a list of "worthiness" or "'True' Power Rangers-ness," all together. To give a Doctor Who example, it would be like trying to arrange your favourite incarnations of "the Doctor," or your favourite companions, by numerically valued order. You can't really definitively value these sorts of things that way without overlooking or ignoring aspects, and eventually ending up with a list that is purely subjective in the eyes of the beholder.
That and I kind of have to agree with the popular consensus here, if I was to write such a list, RPM would definitely be on it.