Green ranger didn't appear till the 30th or so episode of the first season. Died in the japanesse version so that is why he became the white later. Plus it makes sense to save the evil ranger plot for a sequel. Hell you could use the 3 part "green with evil" episodes for two movies if you wanted.. Get us used to the main cast first. He kinda is overrated.. Sure he gets the cool armor and zord, but beyond that once he becomes good he takes out all monsters by himself. That takes out the team aspect. Plus Tommny outside of suit is bland, no character development all that much. Billy had that just lacked the cool suit / zord. How can others be just as good as him when they have a frog for a zord lol.
*Insert snide nerd remark here*