You have a point with Brees, but not Warner or Young. Warner not only played iin a completely different league, but he played well there. Young wasn't bad in the USFL or Tampa.
I'll give you that he has "room to improve" (haha). I do think he'll get better...but I don't see the potential for a "dramatic turnaround." Sure, in the immortal words of Judy Tenudo, "it could happen," but what makes you think that it could? Yeah, he didn't have a great running game and was under considerable pressure a lot--but there were times when he wasn't and he still couldn't hit open WRs.
Don't get me wrong, I don't hate the guy and I'm cool with him being our #2--but I don't get what people see in him other than a big athletic kid (who couldn't hit water if he jumped out of a boat).