And the punishment was meted out by man...because man found God guilty. Wake up.
That's exactly what the Holy Spirit carried Isaiah along to say.
What Isaiah thought about it is neither stated, nor does it matter.
They thought Jesus was being punished by God. They were wrong, but you believe them.
It's not about "viewing" Jesus as sinful, it is about Jesus himself bearing our sins in his body on the tree (2Pe 2:24).
Your unbelief is showing.