Isaiah is describing his appearance, not his intellect. Jesus was clearly a genius, even at age 12. Yes he carried our sin + sorrow; he was also called Rabbi by people who knew about it such as Nicodemus - this is not a ‘courtesy title’.
My post in no way questioned the intellect of the Son of God.
Rather, it was a comment on his line of work and his chosen socio-economic status, as described in scripture.
Moreover, I can’t imagine where you get the idea that anyone who knows scripture would think that Rabbi was a “courtesy title.”
Either you misread, or perhaps you were posting to someone else.