It also can be said that none of the students of the founder reached his level, doesn't matter if they were experienced martial artists before meeting him, or if they crosstrained or if they trained aikido only so your point is a bit moot.
Of course all of them thought aikido was valid, but aikido's validity was no obstacle for them to step outside aikido's box, both technically and philosophical-spiritually.
Ok...Ok... a fair point, sure. How about the fact they gravitated toward Aikido as experienced martial artists and didn't reach the level of O'Sensei. What attracted them to Aikido, as experienced martial artists, what was it in Aikido for them they didn't have?