I believe that article I read about O'Sensei was a fabrication a commonly held perception that size equates to strength when overcome others, as modeled by Sumo, and the laws of physics. And that the "idea" that a person has to be at of an idea weight and shape will affect your Aikido positively is a myth. Per O'Sensei and his top Aikidoka, we see now to exact "ki power" -being defined as physics employed at a high level where muscle strength is out of the equation-has nothing to do directly with BMI. The limitations of movement with someone who is 100+ lbs can interfere, but so does something like arthritis, or other aliments.
I didn't lay that out as well as I should have. Ki power -developing it, using it, and such has nothing to do with weight, size, or hair color. Yes, being 100+ lbs over weight is going to interfere with Aikido movements, just as too much muscle interferes, mass is mass regardless if it is muscle or fat. Yes, the specifics of interference are not identical, but limited motion is limited motion. If your chest is so big due to muscle or fat to limit motion of your arm to complete a technique effectively, than that is an issue. The solution is either adjust the technique to work or abandon it for another. But size large or small can effect Irimi and Tenkan; everyone is different hence employment is not the same for everyone, as they have to adjust to make it effective. That is to say since no two bodies are identical, each individual must make adjustments as a result of their differing body structure, and all that. Weight doesn't effect either of these principles in the same way as a large chest interferes with the full range of movement of the arm during a technique.
Not to get bogged downed on details I will keep things very basic and simple. We assume such limitations as above are a negative with a large person in applying Irimi or Tenkan. Yet, a positive result with a thin person. But having a large body in terms of developing these principle may reduce over-movement, over-correction or over-stepping. Having a large body may reduce the learning curve. Where as going beyond the right point to apply the principles; making greater gross movements are more likely with a thinner person. Add Taisabaki to that as well. Maybe being heavy has its advantage. And yes, the waza of larger person will be different than a thin. But that doesn't mean either is more beneficial than the other. Just that approach and execution of principles and waza are not going to be identical, there will be differences as a result to size differences. One isn't better than the other.
I am not saying this is the absolute, just an observation placed on the table of discussion.