Almost all weapons forms seen now in the west came out of Iwama, and even that didn't happen until Saito wandered out of japan in 1985 or so.
My initial exposure to aikido weapons (1985-6) had a component of Saito, in the form of the 31-count solo kata, but all of my initial instruction in partner practice traces back to Nishio, during the same period. Having subsequently had some additional experience with weapons forms derived from the Nishio, Hikitsuchi, and Saito lines, in addition to those of Saotome Sensei, with which I'm most familiar, I am not convinced of your assertion.
It is fair to say that Saito Sensei's partisans have always had a missionary fervor, not only about Saito Sensei's weapons forms, but about the centrality of those weapons forms to aikido training of all kinds, but there remains a difference between what some wish to be true and what is actually true.
In fact, I don't think it will be clear which approach to aiki-ken and aiki-jo has proved to be the most fit, in terms of survival, for another twenty or thirty years. In the meantime, make mine koryu.
My two cents.