He was NOT cross training to add to some "collection" of techniques called Aikido. Most of which came from his son as a syllabus later-on. he was concerned with testing his real skills against all comers, Sumo, Judo, jujutsu, Koryu kenjutsu, kendo etc.
He was leading and exploring and testing his power, his Aiki
Not doing a collection of techniques to add to his techical base as a cross trainer.
I believe this is the key point in any discussion about cross training vs training methodology/MMA. It is NOT about acquiring a collection of waza. It is about discerning how the principles power the waza and going out and applying those principles against skilled people who don't play by your rules.
For what it is worth, I believe that Ueshiba's anger at the type of practice he witnessed stems not from the fact that the deshi were doing techniques wrong, but rather from the fact that the FOCUS of the training had become the technique.