After Foreman lost to Ali, he was mentally ****ed (See Foreman vs 5 Guys in one night video) Foreman tried to watch his stamina and boxed slowly/cautiously against Young which worked to Youngs favour. Pre Ali Foreman rushes, overpowers and knocks Young out of the ring.
That's total speculation. Young had the boxing style and skills to beat prime Foreman. Just as easily Young with his straight up classic boxing style could have jabbed, held, moved and survived those early rounds and Then came on to make it close or win the decision. Holmes was stronger physically than Young and had a much harder jab and punch. I would bet Holmes would beat George in 78 or thereabouts. In a 15 round bout I'd pick Holmes by late ko.