That was the one and only year I went to all 5 best actor movies. Don't aske me why. In any case, Arkin turned in a masterful performance as John Singer, a deaf mute, and I thought he was a shoe-in for best actor. But nope, Cliff Robertson won for "Charly", a mentally challenged adult subjected to medical experiments. Arkin did the superior job.
I agree with you that Arkin was robbed.
Arkin was excellent. He was positively creepy in Wait Until Dark.