Do you have a source that explains Rav and Shmuel that way. It is a huge Chiddush. I don’t disagree, I just suggested the same in a Shiur a gave this week, but couldn’t find any supporting source. In fact, the Binas Adam 48 clearly does not learn this way. He writes that a red hot milchig pan placed on raw meat does make it Assur because ???? ???.
In fact, it creates a huge problem. If we don’t require a Din of Kli Rishon, why wouldn’t a Kli Sheini Yad Soledes Bo or Iruyi be Mevashel the entire item if we see it became hot. The Beis Yosef on 105:2 writes that there is never Bishul w/o Kli Rishon, implying a “Din” is necessary.
I have a partial answer for this as well, but I want to hear what you think.