Are you an engineer or are you just assuming? Here's a clip from an episode of Modern Marvels where they talk about how all 3 systems of the ride were constructed at the same time because of the scale, none could be added before/after the others.
Youtube Link (it's time stamped to start you right where they begin talking about it) - lasts about 3 minutes or so before they change topics. This episode aired before they even showed the yeti to the public and the ride was still under construction so it's not some retro-fitted BS excuse