The RAF bombers mentioned, the Whitley, Hampden etc., were considered to be the latest in modern military aviation development as were their German counterparts at the outset of war. The ability of cannon firing and eight gun fighters to counter and prevail over the defensive firepower of bombers soon severely dented pre-war expectations. The losses incurred by Bomber Command in the earliest raids were to be repeated time and again and experienced by all combatants on all fronts using all types of bomber aircraft. The B24s and B17s of the USAAF and the Lancasters, Stirlings and Halifax's of Bomber Command and even B29s over the Pacific theatre proved to be just as vulnerable to the cutting edge fighters they faced as those bombers extant in the first year of war.
Unfortunately for the Stirling, the wing design was virtually the same as the Empire 'C' class flying boats and Short Sunderland aircraft. A completely new wing design of say 115+ feet span similar to the slim Davis wing on the B24 and more aerodynamically efficient would have enabled the Stirling to join the ranks of truly war-winning aircraft instead of being encumbered by the original specification which dictated the built-in constraint imposed by the hangars you mentioned.
'Find your enemy and shoot him down - everything else is unimportant.'
