Yeah. Thor was supposed to win Infinity War. He was supposed to kill Thanos and prevent the snap. He knew he could do it and he had the right tool to do it, but he missed. Then he managed to kill the guy after the fact, but doing so didn't actually solve the problem. That's a lot of guilt for one guy to face down. I felt his response was entirely consistent with his character. It's not cowardly; if anything, it makes him more human.