(2) Crosby was important for showing that amplification allowed singers to perform in a conversational, intimate tone. A lot of singers who recorded before Crosby sound like they are shouting out announcements at the top of their lungs.
(3) I agree that Armstrong and Dylan are more important than Crosby. So was Holiday. So was Peggy Lee for that matter.
I'm listening online to Billie right now. Oops, now it's Rod Stewart singing "Time After Time."
http://www.martiniinthemorning.com/Listen_Live_To_Martini_In_The_Morning.htm
I think Bobby Darin is really underrated compared to the other great singers. He was so versatile in his ability to sing multiple genres so convincingly.