One of the things Stan states in that article is that the reason why so many AIkidoka are/were doing stuff that is so different than the Founder's Aikido, is that they only spent a couple of years training with him, and "Certainly this was enough time to become proficient in the art, but not enough to master the vast technical repertoire of Aiki Budo with its many subtleties."
But it would be plenty of time to teach the deshi solo training drills, and get them working on pushing on each other and pushing on walls and stuff, right?
It could be, if he was actively involved on a day to day basis (which he wasn't), or if there weren't a certain caginess in the the teaching process (ala "stealing the techniques"), or if he were more explicit and less "universal" in his instructions to people who didn't have the background to understand the context, etc....
There are (were) a lot of factors in play, if you ask me.
"pushing on each other and pushing on walls and stuff" isn't any easier to teach than anything else, BTW.