Your recurring theme: "Can you name me any qbs who were under THAT MUCH pressure and did not get rattled to a certain extent?" Probably not... because no such thing exists.... and it's also subjective to the extreme.... but no matter because it's utterly nonsensical, IMHO... because I can name hundreds who, EVEN THOUGH "TO SOME EXTENT" got rattled, (as you call it, I would not use that term)... fought through it and succeeded. Fact is - I can't think of any "great" QB who did NOT... and most non-great but good ones as well. Hell, even a few lousy QB's.
One of the reasons I am so behind my grandson's love of the Chargers this year is because Rivers has been doing that "consistently" for nearly his entire career. Again... we can debate that... but it's subjective.