Watched plenty of documentary's on it and I can't say it was ever focused on as a defining part of their what I most fear experience then again I wasn't there and neither were you 
I can assure you, from nearly every account from an American bomber crew in WWII, flak was certainly a defining thing for them.
I was not there, but luckily, hundreds of those who were have shared their memories and journals with others. Some have written books, some have helped write books.
The fact is, more bombers were lost to ack, than to fighters.
I'm sorry the history channel doesn't acknowledge how deadly and feared flak was.
Bombers were regularly shot down by puffy ack at altitudes of 20,000 feet and up.