The butterflies here, had Henry VI been capable of initiating, inspiring and uniting others, are of course many. I'm not certain that a Yorkist challenge wouldn't have occured with a strong & capable H-6 on the throne, though it's likely that it would have been put down rather quickly (maybe). One other note, perhaps who should have said "WI he had been a strong and capable ruler, and had not suffered through bouts of insanity as an adult" or something like that. Henry had many qwirks and was mentally ill, but that doean't make him an idiot.