From Westbrook and Ratti's Aikido and the Dynamic Sphere. The authors quote Tohei in the book.
... the physical techniques can be easily learned within a short time span, like other Martial Arts.]
What exactly should we be focusing on, if not techniques?
According to Sagawa, after
he deigned to "teach" through Kimura, the concept can be grasped very quickly (seventeen in his case) but the achievement of aiki requires "decades" of tanren. What part of "decades" is difficult to understand? Nothing here rebuts that point.
In the case of those whose training incorporates regular kokyu undo and is mindful and rigorous, only the proper application and conceptual or perceptual change is necessary to bring the two into alignment -- as occurred with Tenryu. I contend it is in the nature of a kinesthetic perceptual shift like that of many optical "illusions."
Tenryu had decades of sumo tanren in his background (and Takeda's initial training was sumo, actually, and Ueshiba began in sumo, too). Ueshiba only gave Tenryu the concept with which to shift his perception and then simply apply his innate training to the new perception.
This, I submit, our good friend Rob L. is experiencing. I believe he misjudges his level of inherent preparation. He therefore mistakes the causes of his perceived arc of present gain. Beginning students with significant body movement training would be similarly pre-disposed to make quick gains when exposed to explicit concepts of this type. That could be even non-martial types of training, (Ueshiba's Hokkaido farming and later Aiki-en 合氣園 for example). I have specifically illustrated the similarities of Ark's tanren methods with heavy load-bearing/shifting skills). I have empasized the difference between learning efficient load movement with minimal musclura inputs versus wieghtlifting to build more powerful muscluature.
You assume that there is a necessary order to body training and the conceptual or perceptual shift that is entailed in developing aiki. The history shows that decades of tanren and a conceptual or perceptual shift are required -- and both are necessary to proper aiki. What the history rebuts is that they must occur in a particular order. So on this evidence, the building of body and learning the concept to apply it to are not required to be done in an invariable order. Even if some "poor" aikido training has departed from proper concepts, the tanren aspect in mainline aikido training may not be nearly as lacking as you assume.