I do not beleive your information is correct.
The original advertisements for TF: T Movie included the line "2 years in the making," which only means they were planning on doing a movie in some form at least as long as the cartoon was in existence. Since the original Transformers cartoons were based on pre-existing toys, the original characters were created for the toy line, whereas the movie characters were created for the movie. There's a huge drop-off in the quality of the toys after the first season of the show, and I don't think (given the poor quality of the toys based on characters introduced in the movie) they'd been planning Rodimus Prime or Galvatron for 3 years. The Ultra Magnus toy was just a re-painted Optimus with added accesories to make him look different.