I guess I didn't explain it very well, but here's my best attempt at making it sound sort of plausible.
Every character begins the chapter as their regular civilian base class, but when selected there will be an option to Morph which will be a class skill exclusive to the Rangers. After Morphing, based on the character's Morphing Weapon level, they'll gain a number of stats that is different for each character and team. Once they have Morphed, they will be able to use their specific weapons and abilities.
Promotions will be cut from the game and each Ranger will have a level cap of 40.
Battleizers and Power Ups will be items that the teams can only get at a certain point in the story and can only be used once properly Morphed.
The only promotions I can plausibly see being used are for things like Cam, Doggie Krueger, and other characters who don't start off as Rangers, but who eventually gain powers during the story.