Each of the aiki greats had a few things in common: obsessive/compulsive, stubborn behavior all directed towards training for strength (martial, not physical) and power.
You really think that captures what these guys were doing with their lives? Obsessive-compulsive, consuming drive towards training for "martial strength" and power?
Is that why Ueshiba went to Mongolia to help found a utopia? Because he thought it was a path to internal power?
I think in Ueshiba's case, "martial power" was a trivial, childish goal as he got older. His training was aimed at becoming a conduit of the kami, and to that end his aim was to be able to attain a state of open awareness and a totally uncritical non-consciousness.
As to why some Aikido teachers have reputations as brutes, two words: Imperial Army.